Solaris ZFS
ZFS was designed and implemented by a team at Sun led by
Jeff Bonwick.
It was announced on September 14, 2004. For a humorous
introduction to ZFS' features, see presentation given by Pawel at EuroBSDCon 2007:
http://youtube.com/watch?v=o3TGM0T1CvE.
When ZFS first got started, the outlook for file systems in Solaris was
rather dim. UFS was already nearing the end of its usefulness in terms of file
system size and performance. Many Solaris enterprize customers paid substantial
sums of money to Veritas to run VxFS instead. In a strange way VxFS has become
the enterprise filesystem for Solaris and most job announcements for Solaris
sysadmin jobs included its knowledge as a prerequisite.
Solaris needed a new file system. Jeff Bonwick decided to solve the problem
and started the ZFS project with the organizing metaphor of the virtual memory
subsystem - why can't disk be as easy to administer and use as memory? ZFS has
been based in part on NetApp's sucessful Write
Anywhere File Layout (WAFL)
system. It evolved pretty far from WAFL and now has many differences. This
table lists some of them (please read the blog replies which correct some table
errors.).
The central on-disk data structure was the slab - a chunk of disk divided up
into the same size blocks, like that in the SLAB kernel memory allocator, which
he also created. Instead of extents, ZFS would use one block pointer per block,
but each object would use a different block size - e.g., 512 bytes, or 128KB -
depending on the size of the object. Block addresses would be translated through
a virtual-memory-like mechanism, so that blocks could be relocated without the
knowledge of upper layers. All file system data and metadata would be kept in
objects. And all changes to the file system would be described in terms of
changes to objects, which would be written in a copy-on-write fashion.
ZFS organizes everything on disk into a tree of block pointers, with
different block sizes depending on the object size. ZFS checksums and
reference-counts variable-sized blocks. It write out changes to disk using
copy-on-write - extents or blocks in use are never overwritten in place, they
are always copied somewhere else first.
When it was released with Solaris 10 ZFS broke records in scalability,
reliability, and flexibility.
Although performance is not usually cited as ZFS advantage ZFS is far faster
than most users realize, especially in environments
that involve large number of "typical" files smaller than 5-10 megabytes. The native
support of a volume manager in ZFS is also pretty interesting. That and copy on
write semantics provide
snapshots
which are really important for some applications and for security.
ZFS is one of the few Unix filesystems that
can go neck-to-neck with Microsoft NTFS for performance. Among important
features:
- Simple uniform administration -- one of the biggest selling points.
ZFS is administered by just two commands, zpool and zfs. In ZFS, filesystem
manipulation within a storage pool is easier than volume manipulation within
a traditional filesystem; the time and effort required to create or resize a
ZFS filesystem is closer to that of making a new directory than it is to volume
manipulation in some other systems. This is important because most of ZFS features
are in some form available (layering LVM, md RAID, snapshorts, etc.) However
LVM + filesystem combination introduced the second, entirely different set of
commands and tools to setup and administer the devices. ZFS handles both
layers with a single set of commands and in a simpler manner, as this
PDF
tutorial demonstrates.
- Excellent scalability. 128-bit file system, providing 16 billion
times the capacity of a 64-bit file system
- Integrated management for mounts and NFS sharing
- Pools: slightly more dynamic concept then old volumes. It also makes
a separate LVM layer unnecessary. Each pool can include arbitrary number
of physical disks. Due to built-in striping "combined I/O bandwidth of all devices
in the pool is available to all file systems at all times."
- All operations are copy-on-write transactions -- no need to fsck.
- Disk scrubbing -- live online checking of blocks against their checksums,
and self-repair of any problems. ZFS employs 256 bit checksums end-to-end
to validate data stored under its protection.
- Pipelined I/O -- The pipeline operates on I/O dependency graphs and
provides scoreboarding, priority, deadline scheduling, out-of-order issue and
I/O aggregation." Or in short, improved handling of large loads.
- Snapshots -- A 'read-only point-in-time copy of a filesystem', with
backups being driven using snapshots to allow, rather impressively, not just
full imaging but incremental backups from multiple snapshots. Easy and space
efficient.
- Clones -- writable copies of a snapshot which are an extremely space-efficient
way to store many copies of mostly-shared data. Clones effectively result
in two independent file systems that share a set of blocks.
- Built-in compression -- now available for most other filesystems,
usually as an addon. For large text file such as log files compression can not
only save space, but I/O time. LZJB
is used for compresssion. LZJB is a
lossless data compression
algorithm
invented by
Jeff
Bonwick to compress crash dumps and data in
ZFS. It includes
a number of improvements to the
LZRW1 algorithm,
a member of the
Lempel-Ziv
family of compression algorithms.
- Maintenance and troubleshooting capabilities. Advanced backup and
restore features
- Support of NFSv4 ACL. THe NFSv4 (Network File System – Version 4)
protocol introduces a new ACL (Access Control List) format that extends other
existing ACL formats. NFSv4 ACL is easy to work with and introduces more detailed
file security attributes, making NFSv4 ACLs more secure. NFSv4 ACL has a rich
set of inheritance properties as well as a set of permission bits broader then
classic Unix read, write and execute troika. There are two categories of access
mask bits:
1.) The bits that control the access
to the file
i.e. write_data, read_data, write_attributes, read_attributes
2.) The bits that control the management
of the file
i.e. write_acl, write_owner ZFS NFSv4 implementation provides better interoperability
with other vendor's NFSv4 implementations
- Endian neutrality
ZFS is also supported in Free BSD and Mac OS X (leopard). There are rumors Apple
may be preparing to adopt it as the default filesystem replacing the aging HFS+
in the future.
A good overview is available from BigAdmin Feature Article
ZFS Overview
and Guide
ZFS organizes physical devices into logical pools called storage pools.
Both individual disks and array logical unit numbers (LUNs) visible to the operating
system may be included in a ZFS pools.
...Storage pools can be sets of disks striped
together with no redundancy (RAID 0), mirrored disks (RAID 1),
striped mirror sets (RAID 1 + 0), or striped with parity (RAID Z). Additional
disks can be added to pools at any time but they must be added with the same
RAID level. For example, if a pool is configured with RAID 1, disks may be added
only to the pool in mirrored sets in the same number as was used when the pool
was created. As disks are added to pools, the additional storage is automatically
used from that point forward.
Note: Adding disks to a pool causes data to be written to the new
disks as writes are performed on the pool. Existing data is not redistributed
automatically, but is redistributed when modified.
When organizing disks into pools, the following issues should be considered:
- Disk contention. Use whole disks in storage pools. If
individual disk partitions are used to build a storage pool, contention
could occur between the pool and the partitions not included in the pool.
Never include a disk in more than one storage pool.
- Controller contention. Try to balance anticipated load
across the available controllers. For example, when configuring disks for
an Oracle database, build the pool that will hold the data table spaces
with disks assigned to different controllers than the pool that will hold
index table spaces. A disk's controller number is represented by the number
after the "c" in the disk's device file name (
/dev/dsk/c1t0d0
is a disk on controller 1).
- File system layout. More than one file system can be built
in a single storage pool. Plan the size and composition of pools to accommodate
similar file systems. For example, rather than building 10 pools for 10
file systems, performance will likely be better if you build two pools and
organize the file systems in each pool to prevent contention within the
pools (that is, do not use the same pool for both indexes and table data).
Note: RAID-Z is a special implementation of RAID-5 for ZFS allowing
stripe sets to be more easily expanded with higher performance and availability.
Storage pools perform better as more disks are included.
Include as many disks in each pool as possible and build multiple file systems
on each pool.
ZFS File System
ZFS offers a POSIX-compliant file system interface to the operating system.
In short, a ZFS file system looks and acts exactly like a UFS file system except
that ZFS files can be much larger, ZFS file systems can be much larger, and
ZFS will perform much better when configured properly.
Note: It is not necessary to know how big a file system needs to be
to create it.
ZFS file systems will grow to the size of their storage
pools automatically.
ZFS file systems must be built in one and only one storage pool, but a storage
pool may have more than one defined file system. Each file system in a storage
pool has access to all the unused space in the storage pool. As any one file
system uses space, that space is reserved for that file system until the space
is released back to the pool by removing the file(s) occupying the space. During
this time, the available free space on all the file systems based on the same
pool will decrease.
ZFS file systems are not necessarily managed in the /etc/vfstab
file. Special, logical device files can be constructed on ZFS pools and mounted
using the vfstab file, but that is outside the scope of this guide.
The common way to mount a ZFS file system is to simply define it against a pool.
All defined ZFS file systems automatically mount
at boot time unless otherwise configured.
Finally, the default mount point for a ZFS file system is based on the name
of the pool and the name of the file system. For example, a file system named
data1 in pool indexes would mount as /indexes/data1
by default. This default can be overridden either when the file system is created
or later if desired.
Command-Line Interface
The command-line interface consists primarily of the zfs and
zpool commands.. Using these commands, all the storage devices
in any system can be configured and made available. A graphical interface is
available through the Sun Management Center. Please see the SMC documentation
at docs.sun.com for more information.
For example, assume that a new server named proddb.mydomain.com
is being configured for use as a database server. Tables and indexes must be
on separate disks but the disks must be configured for highly available service
resulting in the maximum possible usable space. On a traditional system, at
least two arrays would be configured on separate storage controllers, made available
to the server by means of hardware RAID or logical volume management (such as
Solaris Volume Manager) and UFS file systems built on the device files offered
from the RAID or logical volume manager. This section describes how this same
task would be done with ZFS.
Planning for ZFS
Tip 2: Use the format
command to determine the list of available devices
and to address configuration problems with those devices.
The following steps must be performed prior to configuring ZFS on a new system.
All commands must be issued by root or by a user with root authority:
- Determine which devices are available to the local system.
Before
configuring ZFS, it is important to be certain what disks are available
to the system.
- Ensure that these devices are properly configured in the operating system.
Different platforms and devices require different configuration steps before
they can be reliably used with the Solaris OS. Consult the documentation
with your storage devices and OS for more information.
- Plan what pools and file systems will be necessary.
Review the expected
use for the system and determine what pools will be necessary and what file
systems will be in each pool. File systems can be migrated from pool to
pool so this does not have to be precise; expect to experiment until the
right balance is struck.
- Determine which devices should be included in which pool.
Match the
list of pools with the list of devices and account for disk and controller
contention issues as well as any hardware RAID already applied to the available
devices.
Additional planning information can be found at
docs.sun.com.
In the running example, two bodies of JBOD ("just a bunch of disks" or non-RAID
managed storage) are attached to the server. Though there is no reason to avoid
hardware RAID systems when using ZFS, this example is clearer without hardware
RAID systems. The following table lists the physical devices presented from
attached storage.
| c2t0d0 |
c4t0d0 |
c3t0d0 |
c5t0d0 |
| c2t1d0 |
c4t1d0 |
c3t1d0 |
c5t1d0 |
| c2t2d0 |
c4t2d0 |
c3t2d0 |
c5t2d0 |
| c2t3d0 |
c4t3d0 |
c3t3d0 |
c5t3d0 |
Based on the need to separate indexes from data, it is decided to use two
pools named indexes and tables, respectively. In order
to avoid controller contention, all the disks from controllers 2 and 4 will
be in the indexes pool and those from controllers 3 and 5 will
be in the tables pool. Both pools will be configured using RAID-Z
for maximum usable capacity.
Creating a Storage Pool
Storage pools are created with the zpool command. Please see
the man page, zpool (1M), for information on all the command options.
However, the following command syntax builds a new ZFS pool:
# zpool create <pool_name> [<configuration>] <device_files>
The command requires the user to supply a name for the new pool and the disk
device file names without path (c#t#d# as opposed to /dev/dsk/c#t#d#).
In addition, if a configuration flag, such as mirror or raidz,
is used, the list of devices will be configured using the requested configuration.
Otherwise, all disks named are striped together with no parity or other highly
available features.
Tip 3: Check out the
-m
option for defining a specific mount point or the
-R option for redefining the relative
root path for the default mount point.
Continuing the example, the zpool commands to build two RAID-Z
storage pools of eight disks, each with minimum controller contention, would
be as follows:
# zpool create indexes raidz c2t0d0 c2t1d0 c2t2d0 \
c2t3d0 c4t0d0 c4t1d0 c4t2d0 c4t3d0
# zpool create tables raidz c3t0d0 c3t1d0 c3t2d0 \
c3t3d0 c5t0d0 c5t1d0 c5t2d0 c5t3d0
The effect of these commands will be to create two pools named indexes
and tables, respectively, each with RAID-Z striping and data redundancy.
ZFS pool names can be named anything starting with a letter except the strings
mirror, raidz, spare, or any string starting
with c# where # is any digit 0 through 9. ZFS pool
names can include only letters, digits, dashes, underscores, or periods.
Creating File Systems
If the default file system that is created is not adequate to suit the needs
of the system, additional file systems can be created using the zfs
command. Please see the man page, zfs (1M), for detailed information
on the command's options.
Suppose, in the running example, two databases were to be configured on the
new storage and for management purposes, each database needed to have its own
mount points in the indexes and tables pools. Use
the zfs command to create the desired file systems as follows:
# zfs create indexes/db1
# zfs create indexes/db2
# zfs create tables/db1
# zfs create tables/db2
Note: Be careful when naming file systems. It is possible to reuse
the same name for different file systems in different pools, which might be
confusing.
The effect is to add a separate mount point for db1 and
db2 under each of /indexes and /tables.
In the mount output, something like the following would be shown:
The space available to /indexes, /indexes/db1,
and /indexes/db2 is all of the space defined in the indexes
pool. Likewise, the space available to /tables, /tables/db1,
and /tables/db2 is all of the space defined in the tables
pool. The file systems db1 and db2 in each pool are
mounted as separate file systems in order to provide distinct control and management
interfaces for each defined file system.
Tip 4: Check out the set
options of the zfs
command to manipulate the mount point and other properties
of each file system.
Displaying Information
Information on the pools and file systems can be displayed using the
list commands for zpool and zfs. Other
commands exist as well. Please read the man pages for zfs and
zpool for the complete list.
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
indexes 240M 110K 240M 0% ONLINE -
tables 240M 110K 240M 0% ONLINE -
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
indexes 107K 208M 25.5K /indexes
indexes/db1 24.5K 208M 24.5K /indexes/db1
indexes/db2 24.5K 208M 24.5K /indexes/db2
tables 107K 208M 25.5K /tables
tables/db1 24.5K 208M 24.5K /indexes/db1
tables/db2 24.5K 208M 24.5K /indexes/db2
Monitoring
Though a detailed discussion of monitoring is out of this document's scope,
this overview would be incomplete without some mention of the ZFS built-in monitoring.
As with management, the command to monitor the system is simple:
# zpool iostat <pool_name> <interval> <count>
This command works very much like the iostat command found in
the operating system. If the pool name is not specified, the command reports
on all defined pools. If no count is specified, the command reports until stopped.
A separate command was needed as the iostat command in the operating
system cannot see the true reads and writes performed by ZFS; it can see only
those submitted to and requested from file systems.
The command output is as follows:
# zpool iostat test_pool 5 10
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
test_pool 80K 1.52G 0 7 0 153K
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
test_pool 80K 1.52G 0 0 0 0
Other commands can be used to contribute to an administrator's understanding
of the status, performance, options, and configuration of running ZFS pools
and file systems. Please read the man pages for zfs and zpool
for more information.
There is ZFS centered
litigation between
NetApps
and Sun.
in 2007 NetApp alleged that Sun violated seven of its patents and demanded Sun
remove its ZFS file system from the open-source community and storage products,
and limit its use to computing devices. Please note that Sun indemnifies all
its customers against IP claims.
In October 2007 Sun counter-sued, saying NetApp infringed 22 of its patents which
puts NetApp in typical for such suits crossfire. Sun
requested the
removal of all NetApp products from the marketplace. It the was a big
present to EMC as the letter below suggests:
To NetApp Employees and Customers on Sun’s Lawsuit
[Note: This is an e-mail that I sent internally to our employees, with
the expectation that they might also share it with customers. Some of it repeats
previous posts, but other parts are different. In the spirit of openness, I
decided to post here as well.]
To: everyone-at-netapp
Subject: Sun's Lawsuit Against NetApp
This morning, Sun filed suit seeking a “permanent
injunction against NetApp” to remove almost all of our products from the
market place. That’s some pretty scary language! It seems designed to make NetApp
employees wonder, Do I still have a job? And customers to wonder,
Is it safe to buy NetApp products?
I’d like to reassure you. Your job is safe. Our products are all still for
sale.
Can you ever remember a Fortune 1000 company being shut down by patents?
It just doesn’t happen! Even for the RIM/Blackberry case, which is the closest
I can think of to a big company being shut down, it took years and years to
get to that point, and was still averted in the end. I think it’s safe to say
the odds of Sun fulfilling their threat are near zero.
If you are a customer, you can be confident buying NetApp products.
If you are an employee, just keep doing your job! Even if your job is to
partner with Sun, keep doing your job. Here’s a ironic story. When James and
I received the
IEEE Storage Systems Award for our work in WAFL and appliances “which has
revolutionized storage”, it was a Sun employee who organized the session where
the award was presented. He was friendly, we were friendly, and we didn’t talk
about the lawsuit. You can do it too. The first minute or two might feel odd,
but then you’ll get over it. We have many joint customers to take care of.
Also NetApp landed on the wrong side of open source debate which will cost them
a lot both in goodwill and actual customers. Old proverb "Those who live
in glass houses should not throw stones" is very relevant here. The shadow
of SCO over NetApp is very real threat to their viability on the marketplace.
As a powerful movement open source community is a factor that weights into all deliberations.
I think Netapp made a mistake here: for companies of approximately equal size
the courtroom really doesn't work well as a venue for battles in storage industry.
Lawsuits about software patent (usually with broad, absurg generalizations included
in the patent) infringement claims are extremely risky ventures that can backfire.
Among near equals, the costly patent enforcement game is essentially a variant of
MAD (mutually-assured destruction).
Biotech companies learned this a long time ago, when they realized that it makes
little sense to sue each other over drug-enabling tech even before FDA approval,
which is the true gating function which confers the desired monopoly and knocks
the other out of the ring. In case of software prior art defense can work wonders
for most so called patents.
After Oracle acquisition of Sun NetApp claims should be reviewed as they politically
NetApp cannot go after Oracle -- the main database that is using NetAPP storage
appliances. Any attempt to extract money from Oracle means a lot of lost revenue
for the company. Unless Oracle does not care about open source ZFS existence,
which is also a possibility.
What is ZFS? Why People Use ZFS? [Explained for Beginners] | It's FOSS
sysadmin:
One pretty good intro to ZFS is here:
http://opensolaris.org/os/community/zfs/whatis/It's a glorified bullet
list with a brief description of what each feature means.
For example, one could quibble on the "snapshot of snapshots" feature:
ZFS backup and restore are powered by snapshots. Any snapshot can generate
a full backup, and any pair of snapshots can generate an incremental
backup. Incremental backups are so efficient that they can be used for
remote replication â€" e.g. to transmit an incremental update every
10 seconds.
It also appears you've left some of the ZFS advantages out of the table
– I'd encourage your readers to see the original blog posting. I don't know
if this is in BTRFS, but it's a lifesaver:
ZFS provides unlimited constant-time snapshots and clones. A snapshot
is a read-only point-in-time copy of a filesystem, while a clone is
a writable copy of a snapshot. Clones provide an extremely space-efficient
way to store many copies of mostly-shared data such as workspaces, software
installations, and diskless clients.
mark_w
I am very glad to see this comparison, but I would like to make a few
comments.
- the title/summary is poor. The comment "Linux don't need no stinkin'
ZFS…“Butter FS†is on the horizon and it’s boasting more features
and better performance" is misleading.
According to your summary table, you have one area in which BTRFS can be
considered more featured than ZFS (snapshots of snapshots). Considering
that you haven't even discussed clones (which maybe do the same thing or
more) and that ZFS is not only a filesystem but it, and its utilities,
integrate the LVM features and it has, right now, a wide selection of
RAID modes that are actually functioning and it does 'automagic'
adaptation to volumes of differing performance values, this seems to be
a claim that you get nowhere near justifying. Maybe, eventually, it will
be true, but the current version doesn't have the features and there is
little evidence that 'first stable release' will either.
(Sorry, I'm not trying to say that BTRFS is 'bad', just that you are
accidentally overclaiming; my guess would be that you haven't read much
on ZFS and all of its features. I think if you had, you would have
realised that BTRFS on its own or in its first stable release isn't
going to do it. BTRFS plus on the fly compression, plus a revised MD,
plus LVM may well, though, but I'm expecting to wait a bit for all of
those to work ideally together.)
- the title leads you to believe that BTRFS will be shown to have a
better performance than ZFS. The actual comparison is between BTRFS and
ext filesystems with various configurations.
- one of the clever features of ZFS is protection against silent data
corruption. This may not be vital to me now, but as filesystem sizes
increase…a colleague deals with the situation in which a research
project grabs nearly 1G of data every day and they have data going back
over 5 years (and they intend to keep capturing data for another 50+
years). As he says "how do I ensure that the data that we read is the
data that we wrote?", and its a good question. ZFS is good in that,
admittedly obscure, situation, but I'm not sure whether BTRFS will be.
- You make (indirectly) the very good point that with the more advanced
filesystems, benchmarking performance can be rather sensitive to set-up
options. I am very glad that you did that testing and hope that you can
do more thorough testing as we get closer to a version 1.0 release. I am
not sure that I can help you with your funding submission, though…
It is also the case that the results that you get are heavily dependant
on what you measure, so the more different tests you do, the better.
- another clever feature of ZFS (sorry about sounding like sounding like
a stuck record, but I am impressed by ZFS and would love to be as
impressed by BTRFS) is that you can make an array incorporating SSDs and
hard disks and have the system automagically sort out the usage of the
various storage types to give an agregate high performance,
low-cost-per-TB, array. In a commercial setting this is probably one of
the biggest advantages that ZFS has over earlier technology. I'm sure
that I don't have to use the 'O' word here, but this is a vital
advantage that Sun has, and I'm expecting to see some interesting work
on optimising this system, in particular for database accesses, soon.
(BTW, this is so effective that a hybrid array, as used in Amber Road,
can be so effective that comparing a hybrid array of SSDs and slow hard
disks can be faster, cheaper and much more power efficient than one
using the usual enterprise class SAS disks, so this can be an
interesting solution, in enterprise apps)
If you wish to know more about ZFS, you can do worse than read Sun's
whitepapers on the subject; search on "sun zfs discovery day" to get
more info; the presentation is very readable. (I'm not, btw, suggesting
that this is an unbiased comparison of ZFS to anything else; its a
description of the features and how-to-use.)
softweyr
One (of the many) mis-understood features of ZFS is how the file
metadata works. In most existing filesystems that support arbitrary
metadata, the metadata space is limited and essentially allows key/data
pairs to be associated with the file. In ZFS, the metadata for each
filesystem object is another entire filesystem rooted at the containing
file. ZFS is, in essence, a 3D filesystem. Consider Apple's application
bundles, currently implemented as a directory that the Finder
application recognizes and displays specially. Using ZFS, the
application file could be the icon file for the application, all of the
component files, including executables, libraries, localization packs,
and other app resources, would be stored in the file metadata. To the
outside world, the bundle truly appears as a single file.
ZFS has it's warts, for instance that storage of small files is quite
inefficient, but actually besting it is going to be a long, hard slog. I
suspect the big commercial Linux distributions will iron out the
licensing issues somehow and including ZFS in their distributions in the
next year. Linux is too big a business to be driven by the religious
zealots anymore.
stoatwblr
2-and-a-bit years on and ZFS is still chugging along nicely as a
working, robust filesystem (and yes, it _does_ have snapshots of
snapshots) which I've found impossible to break.
Meantime, Btrfs has again trashed itself on my systems given scenarios
as simple as power failure.
That's without even going into the joy of ZFS having working ssd read
and write caching out front which substantially boosts performance while
keeping the robustness (even 64Gb is more than adequate for a 10TB
installation I use for testing)
If there's any way of reconciling CDDL and GPL then the best way forward
would be to combine forces. BTRFS has a lot of nice ideas but ZFS has
them too and it has the advantage of a decade's worth of actual real
world deployment experience to draw on.
Less infighting among OSS devs, please.
Some interesting discussion that among other things outlines position of Linuxoids
toward ZFS. Envy is great motivator for findings faults ;-)
ZFS d
ZFS has gotten a lot of hype. It has also gotten some derision from Linux
folks who are accustomed to getting that hype themselves. ZFS is not a magic
bullet, but it is very cool. I like to think that if UFS and ext3 were first
generation UNIX filesystems, and VxFS and XFS were second generation, then ZFS
is the first third generation UNIX FS.
ZFS is not just a filesystem. It is actually a hybrid filesystem and volume
manager. The integration of these two functionalities is a main source of the
flexibility of ZFS. It is also, in part, the source of the famous "rampant layering
violation" quote which has been repeated so many times. Remember, though, that
this is just one developer's aesthetic opinion. I have never seen a layering
violation that actually stopped me from opening a file.
Being a hybrid means that ZFS manages storage differently than traditional
solutions. Traditionally, you have a one to one mapping of filesystems to disk
partitions, or alternately, you have a one to one mapping of filesystems to
logical volumes, each of which is made up of one or more disks. In ZFS, all
disks participate in one storage pool. Each ZFS filesystem has the use of all
disk drives in the pool, and since filesystems are not mapped to volumes, all
space is shared. Space may be reserved, so that one filesystem can't fill up
the whole pool, and reservations may be changed at will. However, if you don't
want to decide ahead of time how big each filesystem needs to be, there is no
need to, and logical volumes never need to be resized. Growing or shrinking
a filesystem isn't just painless, it is irrelevant.
ZFS provides the most robust error checking of any filesystem available.
All data and metadata is checksummed (SHA256 is available for the paranoid),
and the checksum is validated on every read and write. If it fails and a second
copy is available (metadata blocks are replicated even on single disk pools,
and data is typically replicated by RAID), the second block is fetched and the
corrupted block is replaced. This protects against not just bad disks, but bad
controllers and fibre paths. On-disk changes are committed transactionally,
so although traditional journaling is not used, on-disk state is always valid.
There is no ZFS fsck program. ZFS pools may be scrubbed for errors (logical
and checksum) without unmounting them.
The copy-on-write nature of ZFS provides for nearly free snapshot and clone
functionality. Snapshotting a filesystem creates a point in time image of that
filesystem, mounted on a dot directory in the filesystem's root. Any number
of different snapshots may be mounted, and no separate logical volume is needed,
as would be for LVM style snapshots. Unless disk space becomes tight, there
is no reason not to keep your snapshots forever. A clone is essentially a writable
snapshot and may be mounted anywhere. Thus, multiple filesystems may be created
based on the same dataset and may then diverge from the base. This is useful
for creating a dozen virtual machines in a second or two from an image. Each
new VM will take up no space at all until it is changed.
These are just a few interesting features of ZFS. ZFS is not a perfect replacement
for traditional filesystems yet - it lacks per-user quota support and performs
differently than the usual UFS profile. But for typical applications, I think
it is now the best option. Its administrative features and self-healing capability
(especially when its built in RAID is used) are hard to beat.
Note to future
contestants
by sbergman27 on Mon 21st
Apr 2008 20:10 UTC
Member since:
2005-07-24
ZFS has gotten a lot of hype. It has also gotten some derision from Linux
folks who are accustomed to getting that hype themselves.
It would be advisable to stay on topic and edit out any snipey and unprofessional
off-topic asides like the above quoted material. This article is supposed to
be about "Solaris Filesystem Choices". Please talk about Solaris filesystems.
Aside from some understandable concerns about layering, I think most "Linux
folks" recognize that ZFS has some undeniable strengths.
I hope that this Article Contest does not turn into a convenient platform from
which authors feel they can hurl potshots at others.
Edited 2008-04-21 20:25 UTC
Reply Permalink
Score: 9
RE: Note to future
contestants
by jwwf on Mon 21st Apr 2008 21:05
UTC in reply to "Note to future
contestants"
Member since:
2006-01-19
Both of those quoted sentences are factual, and I think it's important to
understand that technology and politics are never isolated subjects.
However, I understand the spirit of your sentiment. In my defense, I wrote the
article both to educate and to entertain. If a person just wants to know about
Solaris filesystems, the Sun docs are way better than anything I might write.
Reply
Permalink
Score: 9
RE[2]: Note to
future contestants
by anomie on Tue 22nd Apr 2008
17:03 UTC in reply to "RE: Note
to future contestants"
Member since:
2007-02-26
Both of those quoted sentences are factual...
Let's not confuse facts with speculation.
You wrote: "It has also gotten some derision from Linux folks who are accustomed
to getting that hype themselves."
In interpretive writing, you can establish that "[ZFS] has gotten some derision
from Linux folks" by providing citations (which you did not provide, actually).
But appending "... who are accustomed to getting that hype themselves" is tacky
and presumptuous. Do you have references to demonstrate that Linux advocates
deride ZFS specifically because they are not "getting hype"? If not, this is
pure speculation on your part. So don't pretend it is fact.
Moreover, referring to "Linux folks" in this context is to make a blanket generalization.
Member since:
2006-01-19
"Both of those quoted sentences are factual...
Let's not confuse facts with speculation.
You wrote: "It has also gotten some derision from Linux folks who are accustomed
to getting that hype themselves."
In interpretive writing, you can establish that "[ZFS] has gotten some derision
from Linux folks" by providing citations (which you did not provide, actually).
But appending "... who are accustomed to getting that hype themselves" is tacky
and presumptuous. Do you have references to demonstrate that Linux advocates
deride ZFS specifically because they are not "getting hype"? If not, this is
pure speculation on your part. So don't pretend it is fact.
Moreover, referring to "Linux folks" in this context is to make a blanket generalization.
"
+1. The author of this article is clearly a tacky, presumptuous speculator,
short on references and long on partisanship.
Seriously, I know I shouldn't reply here, but in the light of the above revelation,
I will. It is extremely silly to turn this into some semantic argument on whether
I can find documentation on what is in someone's heart. If I could find just
two 'folks' who like linux and resent non-linux hype relating to ZFS, it would
make my statement technically a fact. Are you willing to bet that these two
people don't exist?
Yet, would this change anything? No, it would be complete foolishness. Having
spent my time in academia, I am tired of this kind of sophistry of "demonstrating
facts". I read, try things, form opinions, write about it. You have the same
opportunity.
Reply Permalink
Score: 2
RE[4]: Note to future
contestants
by sbergman27 on Tue 22nd
Apr 2008 18:33 UTC in reply to "RE[3]:
Note to future contestants"
Member
since:
2005-07-24
I figure that with popularity comes envy of that popularity. And with that
comes potshots. Ask any celebrity. As Morrissey sings, "We Hate It When Our
Friends Become Successful".
http://www.oz.net/~moz/lyrics/yourarse/wehateit.htm
It's probably best to simply expect potshots to be taken at Linux and Linux
users and accept them with good grace. Politely pointing out the potshots is
good form. Drawing them out into long flame-threads (as has not yet happened
here) is annoying to others and is thus counterproductive. It just attracts
more potshots.
Edited 2008-04-22 18:41 UTC
Reply Permalink
Score: 2
RE[5]:
Note to future contestants
by jwwf on Tue 22nd Apr 2008 19:16
UTC in reply to "RE[4]: Note to
future contestants"
Member since:
2006-01-19
I figure that with popularity comes envy of that popularity. And with that comes
potshots. Ask any celebrity. As Morrissey sings, "We Hate It When Our Friends
Become Successful".
http://www.oz.net/~moz/lyrics/yourarse/wehateit.htm
It's probably best to simply expect potshots to be taken at Linux and Linux
users and accept them with good grace. Politely pointing out the potshots is
good form. Drawing them out into long flame-threads (as has not yet happened
here) is annoying to others and is thus counterproductive. It just attracts
more potshots.
Certainly this happens. On the other hand, who would be better than a celebrity
to demonstrate the "because I am successful, I must be brilliant" fallacy we
mere mortals are susceptible to. I think we would both agree that the situation
is complicated.
Myself, I believe that a little bias can be enjoyable in a tech article, if
it is explicit. It helps me understand the context of the situation--computing
being as much about people as software.
Reply Permalink
Score: 3
RE[4]:
Note to future contestants
by anomie on Tue 22nd Apr 2008
19:52 UTC in reply to "RE[3]:
Note to future contestants"
Member since:
2007-02-26
The author of this article is clearly a tacky, presumptuous speculator
Don't twist words. My comments were quite obviously in reference to a particular
sentence. (I'd add that I enjoyed the majority of your essay.)
If I could find just two 'folks' who like linux and resent non-linux hype
relating to ZFS, it would make my statement technically a fact.
Facts are verifiable through credible references. This is basic Supported Argument
101.
Having spent my time in academia, I am tired of this kind of sophistry of
"demonstrating facts".
Good god, man. What academic world do you come from where you don't have to
demonstrate facts? You're the one insisting that your statements are
fact.
Sure you're entitled to your opinion. But don't confuse facts with speculation.
That is all.
edit: added comment
RE[2]: ZFS is a
dead end.
by Arun on Wed 23rd Apr 2008
23:13 UTC in reply to "RE: ZFS
is a dead end."
Member since:
2005-07-07
Can't say I disagree. The layering violations are more important than some
people realise, and what's worse is that Sun didn't need to do it that way.
They could have created a base filesystem and abstracted out the RAID, volume
management and other features while creating consistent looking userspace tools.
Please stop parroting one Linux developer's view. Go look at the ZFS docs. ZFS
is layered. Linux developers talk crap about every thing that is not linux.
Classic NIH syndrome.
ZFS was designed to make volume management and filesystems easy to use and bulletproof.
What you and linux guys want defeats that purpose and the current technologies
in linux land illustrate that fact to no end.
The all-in-one philosophy makes it that much more difficult to create other
implementations of ZFS, and BSD and Apple will find it that much more difficult
to do - if at all really. It makes coexistence with other filesystems that much
more difficult as well, with more duplication of similar functionality. Despite
the hype surrounding ZFS by Sun at the time of Solaris 10, ZFS still isn't Solaris'
main filesystem by default. That tells you a lot.
That's just plain wrong. ZFS is working fine on BSD and OS X. ZFS doesn't make
coexistence with other filesystems difficult. On my Solaris box I have UFS and
ZFS filesytems with zero problems. In fact I can create a zvol from my pool
and format it with UFS.
RE[2]: Comment
by agrouf
It's not just that. It's maintainability. When features get added to the
wrong layer, it means code redundancy, wasted developer effort, wasted memory,
messy interfaces, and bugs that get fixed in one filesystem, but remain
in the others. It does make a difference just how many filesystems you care about supporting.
The Linux philosophy is to have one that is considered standard, but to
support many. If Sun is planning for ZFS to be the "be all and end all"
filesystem for *Solaris, it is easy to see them coming to a different determination
regarding proper layering. Neither determination is wrong. They just have
different consequences.
Perhaps btrfs will someday implement all of ZFS's goodness in the Linux
Way. I confess to being a bit impatient with the state of Linux filesystems
today. But not enough to switch to Solaris. I guess one can't expect to
have everything.
This is a good, balanced explanation. I think the question is whether the features
provided by ZFS are best implemented in a rethought storage stack. In my opinion,
the naming of ZFS is a marketing weakness. I would prefer to see something like
"ZSM", expanding to "meaningless letter storage manager". Calling it a FS makes
it easy for people to understand, but usually to understand incorrectly. I see ZFS as a third generation storage manager, following partitioned disks
and regular LVMs. Now, if the ZFS feature set can be implemented on a second
generation stack, I say, more power to the implementors. But the burden of proof
is on them, and so far it has not happened.
I too am impatient with the state of Linux storage management. For better or
worse, I just don't think it is a priority for the mainline kernel development
crew, or Red Hat, which, like it or not, is all that matters in the commercial
space. I think ext3 is a stable, well-tuned filesystem, but I find LVM and MD
to be clumsy and fragile. Once ext4 is decently stable, I would love to see
work on a Real Volume Manager (tm).
April 16, 2009 |
E O N
Using
EON/Opensolaris and ZFS for storage
will at some point cause you to cross paths with NFSv4 Access Control Lists.
The control available through ACLs are really granular and powerful but they
are also hard to manage and a bit confusing. Here i'll share my methods of handling
ACLs which requires some pre-requisite reading to help understand the
Compact
Access codes:add_file w, add_subdirectory p, append_data p, delete d , delete_child D , execute x , list_directory r , read_acl c , read_attributes a , read_data r , read_xattr R , write_xattr W , write_data w , write_attributes A , write_acl C , write_owner o
Inheritance
compact codes:(remember i on a directory causes a recursive inheritance)file_inherit f , dir_inherit d , inherit_only i , no_propagate n
ACL set codes:full_set = rwxpdDaARWcCos = all permissions
modify_set = rwxpdDaARWc--s = all permissions except write_acl, write_owner
read_set = r-----a-R-c--- = read_data, read_attributes, read_xattr, read_acl
write_set = -w-p---A-W---- = write_data, append_data, write_attributes, write_xattr
If I create a file/folder (foo) via a windows client on a SMB/CIFS share the
permissions typically resemble.eon:/deep/tank#ls -Vd foo
d---------+ 2 admin stor 2 Apr 20 14:12 foo
user:admin:rwxpdDaARWcCos:-------:allow
group:2147483648:rwxpdDaARWcCos:-------:allow
This works fine for the owner (admin) but in a case where multiple people (family)
use the storage, adding user access and more control over sharing is usually
required. So how do I simply add the capability needed? If I wish to modify
this(above), I always start by going back to default valueseon:/deep/tank#chmod A- foo
eon:/deep/tank#ls -Vd foo
d--------- 2 admin stor 2 Apr 20 14:12 foo
owner@:rwxp----------:-------:deny
owner@:-------A-W-Co-:-------:allow
group@:rwxp----------:-------:deny
group@:--------------:-------:allow
everyone@:rwxp---A-W-Co-:-------:deny
everyone@:------a-R-c--s:-------:allow
I then copy and paste them directly into a terminal or script (vi /tmp/bar)
for trial and error and simply flip the bits I wish to test on or off. Note
I'm using A= which will wipe and replace with whatever I define. With A+ or
A-, it adds or removes the matched values. So my script will look like this
after the above is copiedchmod -R A=\
owner@:rwxp----------:-------:deny,\
owner@:-------A-W-Co-:-------:allow,\
group@:rwxp----------:-------:deny,\
group@:--------------:-------:allow,\
everyone@:rwxp---A-W-Co-:-------:deny,\
everyone@:------a-R-c--s:-------:allow \
foo
Let's modify group:allow to have write_set = -w-p---A-W----chmod -R A=\
owner@:rwxp----------:-------:deny,\
owner@:-------A-W-Co-:-------:allow,\
group@:--------------:-------:deny,\
group@:-w-p---A-W----:-------:allow,\
everyone@:rwxp---A-W-Co-:-------:deny,\
everyone@:------a-R-c--s:-------:allow \
foo
Running the aboveeon:/deep/tank#sh -x /tmp/bar
+ chmod -R A=owner@:rwxp----------:-------:deny,owner@:-------A-W-Co-:-------:allow,group@:--------------:-------:deny,group@:-w-p---A-W----:-------:allow,everyone@:rwxp---A-W-Co-:-------:deny,everyone@:------a-R-c--s:-------:allow foo
eon:/deep/tank#ls -Vd foo/
d----w----+ 2 admin stor 2 Apr 20 14:12 foo/
owner@:rwxp----------:-------:deny
owner@:-------A-W-Co-:-------:allow
group@:--------------:-------:deny
group@:-w-p---A-W----:-------:allow
everyone@:rwxp---A-W-Co-:-------:deny
everyone@:------a-R-c--s:-------:allow
Adding a user (webservd) at layer 5, 6 with full_set permissionseon:/deep/tank#eon:/deep/tank#chmod A+user:webservd:full_set:d:allow,user:webservd:full_set:f:allow foo
eon:/deep/tank#ls -Vd foo
d----w----+ 2 admin stor 2 Apr 20 14:12 foo
user:webservd:rwxpdDaARWcCos:-d-----:allow
user:webservd:rwxpdDaARWcCos:f------:allow
owner@:rwxp----------:-------:deny
owner@:-------A-W-Co-:-------:allow
group@:--------------:-------:deny
group@:-w-p---A-W----:-------:allow
everyone@:rwxp---A-W-Co-:-------:deny
everyone@:------a-R-c--s:-------:allow
Ooops, that's level 1, 2 so let's undo this by simply repeating the command
with A- instead of A+. Then lets fix it by repeating the command with A5+ instead
of A-eon:/deep/tank#chmod A-user:webservd:full_set:d:allow,user:webservd:full_set:f:allow foo
eon:/deep/tank#ls -Vd foo
d----w----+ 2 admin stor 2 Apr 20 14:12 foo
owner@:rwxp----------:-------:deny
owner@:-------A-W-Co-:-------:allow
group@:--------------:-------:deny
group@:-w-p---A-W----:-------:allow
everyone@:rwxp---A-W-Co-:-------:deny
everyone@:------a-R-c--s:-------:allow
eon:/deep/tank#chmod A5+user:webservd:full_set:d:allow,user:webservd:full_set:f:allow foo
eon:/deep/tank#ls -Vd foo
d----w----+ 2 admin stor 2 Apr 20 14:12 foo
owner@:rwxp----------:-------:deny
owner@:-------A-W-Co-:-------:allow
group@:--------------:-------:deny
group@:-w-p---A-W----:-------:allow
everyone@:rwxp---A-W-Co-:-------:deny
user:webservd:rwxpdDaARWcCos:-d-----:allow
user:webservd:rwxpdDaARWcCos:f------:allow
everyone@:------a-R-c--s:-------:allow
This covers adding, deleting, modifying and replacing NFSv4 ACLs. Hope that
provides some guidance in case you have to tangle with NFSv4 ACLs. The more
exercise you get with NFSv4 ACLs the more familiar you'll be with getting it
to do what you want.
The ZFS file system uses a pure ACL model, that is compliant with the NFSv4
ACL model. What is meant by pure ACL model, is that every file always
has an ACL, unlike file systems such as UFS that have either an ACL or it has
permission bits. All access control decisions are governed by a file's
ACL. All file's still have permission bits, but they are constructed by
analyzing a file's ACL.
NFSv4 ACL Overview
The ACL model in NFSv4 is similar to the Windows ACL model. The NFSv4
ACL model supports a rich set of access permissions and inheritance controls.
An ACL in this model is composed of an array of access control entries (ACE).
Each ACE specifies the permissions, access type, inheritance flags and to whom
the entry applies. In the NFSv4 model the "who" argument of each ACE,
may be either a username or groupname. There are also a set of commonly
know names, such as "owner@", "group@", "everyone@". These abstractions
are used by UNIX variant operating systems to indicate if the ACE is for the
file owner, file group owner or for the world. The everyone@ entry is
not equivalent to the POSIX "other" class, it really is everyone. The
complete description of the NFSv4 ACL model is availabe in Section 5.11 of the
NFSv4 protocol specification.
NFSv4 Access Permissions
Permission
|
Description
|
read_data
|
Permission to read the data of the file
|
list_data
|
Permission to list the contents of a directory
|
write_data
|
Permission to modify the file's data anywhere in the file's offset
range. This includes the ability to grow the file or write to
an arbitrary offset.
|
add_file
|
Permission to add a new file to a directory
|
append_data
|
The ability to modify the data, but only starting at EOF.
|
add_subdirectory
|
Permission to create a subdirectory to a directory
|
read_xattr
|
The ability to read the extended attributes of a file or to do a
lookup in the extended attributes directory.
|
write_xattr
|
The ability to create extended attributes or write to the extended
attributes directory.
|
execute
|
Permission to execute a file
|
delete_child
|
Permission to delete a file within a directory
|
read_attributes
|
The ability to read basic attributes (non-ACLs) of a file.
Basic attributes are considered the stat(2) level attributes.
|
write_attributes
|
Permission to change the times associated with a file or directory
to an arbitrary value
|
delete
|
Permission to delete a file
|
read_acl
|
Permission to read the ACL
|
write_acl
|
Permission to write a file's ACL
|
write_owner
|
Permission to change the owner or the ability to execute chown(1)
or chgrp(1)
|
synchronize
|
Permission to access a file locally at the server with synchronous
reads and writes.
|
NFSv4 Inheritance flags
Inheritance Flag
|
Description
|
file_inherit
|
Can be place on a directory and indicates that this ACE should be
added to each new non-directory file created.
|
dir_inherit
|
Can be placed on a directory and indicates that this ACE should
be added to each new directory created.
|
inherit_only
|
Placed on a directory, but does not apply to the directory itself,
only to newly created files and directories. This flag requires
file_inherit and or dir_inherit to indicate what to inherit.
|
no_propagate
|
Placed on directories and indicates that ACL entries should only
be inherited to one level of the tree. This flag requires file_inherit
and or dir_inherit to indicate what to inherit.
|
NFSv4 ACLs vs POSIX
The difficult part of using the NFSv4 ACL model was trying to still preserve
POSIX compliance in the file system. POSIX allows for what it calls "additonal"
and "alternate" access methods. An additional access method is defined
to be layered upon the file permission bits, but they can only further restrict
the standard access control mechanism. The alternate file access control
mechanism is defined to be independent of the file permission bits and which
if enabled on a file may either restrict or extend the permissions of a given
user. Another major distinction between the additional and alternate access
control mechanisms is that, any alternate file access control mechanism must
be disabled after the file permission bits are changed with a chmod(2).
Additional mechanisms do not need to be disabled when a chmod is done.
Most vendors that have implemented NFSv4 ACLs have taken the approach of "discarding"
ACLs during a chmod(2). This is a bit heavy handed, since a user went
through the trouble of crafting a bunch of ACLs, only to have chmod(2) come
through and destroy all of their hard work. It was this single issue that
was the biggest hurdle to POSIX compliance with ZFS in implementing NFSv4 ACLs.
In order to achieve this Sam,
Lisa and I spent far too long trying
to come up with a model that would preserve as much of the original ACL, while
still being useful. What we came up with is a model that retains
additional access methods, and disabled, but doesn't delete alternate access
controls. Sam and
Lisa have filed an
internet draft which has the details about the chmod(2) algorithm and how
to make NFSv4 ACLs POSIX complient.
So whats cool about this
Lets assume we have the following directory /sandbox/test.dir.
Its initial ACL looks like: %
ls -dv
test.dir
drwxr-xr-x 2 ongk bin
2 Nov 15 14:11 test.dir
0:owner@::deny
1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
/append_data/write_xattr/execute/write_attributes/write_acl
/write_owner:allow
2:group@:add_file/write_data/add_subdirectory/append_data:deny
3:group@:list_directory/read_data/execute:allow
4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
/write_attributes/write_acl/write_owner:deny
5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
/read_acl/synchronize:allow
Now if I want to give "marks" the ability to create files, but not subdirectories
in this
directory then the following ACL would achieve this.
First lets make sure "marks" can't currently create files/directories
$ mkdir /sandbox/bucket/test.dir/dir.1
mkdir: Failed to make directory "/sandbox/test.dir/dir.1"; Permission
denied
$ touch /sandbox/test.dir/file.1
touch: /sandbox/test.dir/file.1 cannot create
Now lets give marks add_file permission
%
chmod
A+user:marks:add_file:allow /sandbox/test.di
%
ls -dv
test.dir
drwxr-xr-x+ 2 ongk bin
2 Nov 15 14:11 test.dir
0:user:marks:add_file/write_data:allow
1:owner@::deny
2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
/append_data/write_xattr/execute/write_attributes/write_acl
/write_owner:allow
3:group@:add_file/write_data/add_subdirectory/append_data:deny
4:group@:list_directory/read_data/execute:allow
5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
/write_attributes/write_acl/write_owner:deny
6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
/read_acl/synchronize:allow
Now lets see if it works for user "marks"
$ id
uid=76928(marks) gid=10(staff) $ touch file.1
$
ls -v
file.1
-rw-r--r-- 1 marks staff
0 Nov 15 10:12 file.1
0:owner@:execute:deny
1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
/write_acl/write_owner:allow
2:group@:write_data/append_data/execute:deny
3:group@:read_data:allow
4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
/write_acl/write_owner:deny
5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
:allow
Now lets make sure "marks" can't create directories.
$ mkdir dir.1
mkdir: Failed to make directory "dir.1"; Permission denied
The write_owner permission is handled in a special way. It allows for
a user to "take" ownership of a file. The following example will help
illustrate this. With the write_owner a user can only do a chown(2) to
himself or to a group that he is a member of.
We will start out with the following file.
%
ls -v
file.test
-rw-r--r-- 1 ongk staff
0 Nov 15 14:22 file.test
0:owner@:execute:deny
1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
/write_acl/write_owner:allow
2:group@:write_data/append_data/execute:deny
3:group@:read_data:allow
4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
/write_acl/write_owner:deny
5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
:allow
Now if user "marks" tries to chown(2) the file to himself he
will get an error.
$ chown marks file.test
chown: file.test: Not owner
$ chgrp staff file.test
chgrp: file.test: Not owner
Now lets give "marks" explicit write_owner permission.
%
chmod
A+user:marks:write_owner:allow file.test
% ls -v file.test
-rw-r--r--+ 1 ongk staff
0 Nov 15 14:22 file.test
0:user:marks:write_owner:allow
1:owner@:execute:deny
2:owner@:read_data/write_data/append_data/write_xattr/write_attributes
/write_acl/write_owner:allow
3:group@:write_data/append_data/execute:deny
4:group@:read_data:allow
5:everyone@:write_data/append_data/write_xattr/execute/write_attributes
/write_acl/write_owner:deny
6:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
:allow
Now lets see who "marks" can chown the file to.
$ id
uid=76928(marks) gid=10(staff)
$ groups
staff storage
$ chown bin file.test
chown: file.test: Not owner
So "marks" can't give the file away.
$ chown marks:staff file.test
Now lets look at an example to show how a user can be granted special delete
permissions. ZFS doesn't create any delete permissions when a file is
created, instead it uses write_data/execute for permission to write to a directory
and execute to search the directory.
Lets first create a read-only directory and then give "marks"
the ability to delete files.
%
ls -dv
test.dir
dr-xr-xr-x 2 ongk bin
2 Nov 15 14:11 test.dir
0:owner@:add_file/write_data/add_subdirectory/append_data:deny
1:owner@:list_directory/read_data/write_xattr/execute/write_attributes
/write_acl/write_owner:allow
2:group@:add_file/write_data/add_subdirectory/append_data:deny
3:group@:list_directory/read_data/execute:allow
4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
/write_attributes/write_acl/write_owner:deny
5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
/read_acl/synchronize:allow
Now the directory has the following files:
%
ls -l
total 3
-r--r--r-- 1 ongk bin
0 Nov 15 14:28 file.1
-r--r--r-- 1 ongk bin
0 Nov 15 14:28 file.2
-r--r--r-- 1 ongk bin
0 Nov 15 14:28 file.3
Now lets see if "marks" can delete any of the files?
$ rm file.1
rm: file.1: override protection 444 (yes/no)? y
rm: file.1 not removed: Permission denied
Now lets give "marks" delete permission on just file.1
%
chmod
A+user:marks:delete:allow file.1
%
ls -v
file.1
-r--r--r--+ 1 ongk bin
0 Nov 15 14:28 file.1
0:user:marks:delete:allow
1:owner@:write_data/append_data/execute:deny
2:owner@:read_data/write_xattr/write_attributes/write_acl/write_owner
:allow
3:group@:write_data/append_data/execute:deny
4:group@:read_data:allow
5:everyone@:write_data/append_data/write_xattr/execute/write_attributes
/write_acl/write_owner:deny
6:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
:allow
$ rm file.1
rm: file.1: override protection 444 (yes/no)? y
Lets see what a chmod(1) that changes the mode would do to a file with a ZFS
ACL.
We will start out with the following ACL which gives user bin read_data and
write_data permission.
$
ls -v
file.1
-rw-r--r--+ 1 marks staff
0 Nov 15 10:12 file.1
0:user:bin:read_data/write_data:allow
1:owner@:execute:deny
2:owner@:read_data/write_data/append_data/write_xattr/write_attributes
/write_acl/write_owner:allow
3:group@:write_data/append_data/execute:deny
4:group@:read_data:allow
5:everyone@:write_data/append_data/write_xattr/execute/write_attributes
/write_acl/write_owner:deny
6:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
:allow
$
chmod
640 file.1
$
ls -v
file.1
-rw-r-----+ 1 marks staff
0 Nov 15 10:12 file.1
0:user:bin:write_data:deny
1:user:bin:read_data/write_data:allow
2:owner@:execute:deny
3:owner@:read_data/write_data/append_data/write_xattr/write_attributes
/write_acl/write_owner:allow
4:group@:write_data/append_data/execute:deny
5:group@:read_data:allow
6:everyone@:read_data/write_data/append_data/write_xattr/execute
/write_attributes/write_acl/write_owner:deny
7:everyone@:read_xattr/read_attributes/read_acl/synchronize:allow
In this example ZFS has prepended a deny ACE to take away write_data
permission. This
is an example of disabling "alternate" access methods.
More details about
how ACEs are disabled are described in
internet draft.
The
ZFS admin guide and the
chmod(1) manpages have many more examples of setting ACLs and how the inheritance
model works.
With the ZFS ACL model access control is no longer limited to the simple "rwx"
model that UNIX has used since its inception.
Over the last several months, I've been doing a lot of work with NFSv4 ACLs.
First, I worked with Sam to get NFSv4
ACL support into Solaris 10. The major portion of this work involved implementing
the pieces to be able to pass ACLs over-the-wire as defined by section 5.11
of the NFSv4 specification
(RFC3530) and the
translators
(code to translate from UFS
(or also referred to as POSIX-draft) ACLs to NFSv4 ACLs and back). At
that point, Solaris was further along with regard to ACLs than it ever had been,
but was still not able to support the full semantics of NFSv4 ACLs. So...here
comes ZFS!After getting the support for NFSv4 ACLs into Solaris 10, I started working
on the ZFS ACL model with Mark and
Sam. So, you might wonder why a couple of NFS people (Sam and I) would
be working with ZFS (Mark) on the ZFS ACL model...well that is a good question.
The reason for that is because ZFS has implemented native NFSv4 ACLs.
This is really exciting because it is the first time that Solaris is able to
support the full semantics of NFSv4 ACLs as defined by RFC3530.
In order to implement native NFSv4 ACLs in ZFS, there were a lot of problems
we had to overcome. Some of the biggest struggles were ambiguities in
the NFSv4 specification and the requirement for ZFS to be POSIX compliant.
These problems have been captured in an
Internet Draft submitted by Sam and me on October 14, 2005.
ACLs in
the Computer Industry:
What makes NFSv4 ACLs so special...so special to have the shiny, new ZFS implement
them? No previous attempt to specify a standard for ACLs has succeeded,
therefore, we've seen a lot of different (non-standard) ACL models in the industry.
With NFS Version 4, we now have an IETF approved
standard for ACLs.As well as being a standard, the NFSv4 ACL model is very powerful. It
has a rich set of inheritance properties as well as a rich set of permission
bits outside of just read, write and execute (as explained in the Access mask
bits section below). And for the Solaris NFSv4 implementation this means
better interoperability with other vendor's NFSv4 implementations.
ACLs
in Solaris:
Like I said before, ZFS has native NFSv4 ACLs! This means that ZFS can
fully support the semantics as defined by the NFSv4 specification (with the
exception of a couple things, but that will be mentioned later).What makes
up an ACL?
ACLs are made up of zero or more Access Control Entries (ACEs). Each ACE
has multiple components and they are as follows:1.) Type component:
The type component of the ACE defines
the type of ACE. There
are four types of ACEs: ALLOW, DENY,
AUDIT, ALARM.
The ALLOW type ACEs permit access.
The DENY type ACES restrict access.
The AUDIT type ACEs audit accesses.
The ALARM type ACEs alarm accesses.
The ALLOW and DENY type of ACEs are implemented
in ZFS.
AUDIT and ALARM type of ACEs are not
yet implemented in ZFS.
The possibilities of the AUDIT and ALARM
type ACEs are described below. I
wanted to explain the flags that need
to be used in conjunction with them before
going into any detail on what they do,
therefore, I gave this description its own
section.
2.) Access mask bits component:
The access mask bit component of the
ACE defines the accesses
that are controlled by the ACE.
There are two categories of access mask
bits:
1.) The bits that control the access
to the file
i.e. write_data, read_data, write_attributes, read_attributes
2.) The bits that control the management
of the file
i.e. write_acl, write_owner
For an explanation of what each of the
access mask bits actually control in ZFS,
check out
Mark's blog.
3.) Flags component:
There are three categories of flags:
1.) The bits that define inheritance
properties of an ACE.
i.e. file_inherit, directory_inherit, inherit_only,
no_propagate_inherit
Again, for an explanation of these flags, check out
Mark's blog.
2.) The bits that define whether or not
the ACE applies to a user or group
i.e. identifier_group
3.) The bits that work in conjunction
with the AUDIT and ALARM type ACEs
i.e. successful_access_flag, failed_access_flag.
ZFS doesn't support these flags since they don't support AUDIT and
ALARM type ACEs.
4.) who component:
The who component defines the entity
that the ACE applies to.
For NFSv4, this component is a string
identifier and it can be a user, group or
special identifier (OWNER@, GROUP@, EVERYONE@).
An important thing to
note about the EVERYONE@ special identifier
is that it literally means everyone
including the file's owner and owning
group. EVERYONE@ is not equivalent to
the UNIX other entity. (If you
are curious as to why NFSv4 uses strings rather
than integers (uids/gids), check out
Eric's blog.)
For ZFS, this component is an integer
(uid/gid).
What do AUDIT and ALARM ACE types do?
The AUDIT and ALARM type of ACES trigger an audit or alarm event upon the successful
or failed accesses depending on the presence of the successful/failed
access flags (described above) as defined in the access mask bits of the
ACE. The ACEs of type AUDIT and ALARM don't play a role when doing
access checks on a file. They only define an action to happen in the event
that a certain access is attempted. For example, lets say we have the following ACL:
lisagab:write_data::deny
lisagab:write_data:failed_access_flag:alarm
The first ACE affects the access that user, "lisagab", has to the file.
The second ACE says if user, "lisagab", attempts to access this file for writing
and fails, trigger an alarm event. One important thing to remember is the fact that what we do in the event of
auditing or alarming is still undefined. Although, you can think
of it like this: when the access in question happens, auditing could be the
logging the event to a file and alarming could be the sending of an email to
an administrator.
How is access checking done?
To quote the NFSv4 specification: To determine if a request succeeds, each nfsace4 entry is processed
in order by the server. Only ACEs which have a "who" that matches
the requester are considered. Each ACE is processed until all of the
bits of the requester's access have been ALLOWED. Once a bit (see
below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
considered in the processing of later ACEs. If an ACCESS_DENIED_ACE
is encountered where the requester's access still has unALLOWED bits
in common with the "access_mask" of the ACE, the request is denied.
What this means is:The most important thing to note about access checking
with NFSv4 ACLs is that it is very order dependent. If a request for access
is made, each ACE in the ACL is traversed in order. The first ACE that
matches the who of the requester and defines the access that is being requested
is honored.
For example, lets say user, "lisagab", is requesting the ability to read the
data of file, "foo" and "foo" has the following ACL:
everyone@:read_data::allow
lisagab:write_data::deny
lisagab would be allowed the ability to read_data because lisagab is covered
by "everyone@".Another thing that is important to know is that the access determined is cumulative.
For example, lets say user, "lisagab", is requesting the ability to read and
write the data of file, "bar" and "bar" has the following ACL:
lisagab:read_data::allow
lisagab:write_data::allow
lisagab would be allowed the ability to read_data and write_data.How to
use ZFS/NFSv4 ACLs on Solaris:
Many of you may remember the setfacl(1) and getfacl(1) commands. Well,
those are still around, but won't help you much with manipulating ZFS or pure
NFSv4 ACLs. Those commands are only capable of manipulating the POSIX-draft
ACLs as implemented by UFS.As a part of the ZFS putback, Mark has modified the
chmod(1) and
ls(1) command line utilities in order to manipulate ACLs on Solaris.
chmod(1) and ls(1) now give us the ability to manipulate ZFS/NFSv4 ACLs.
Interestingly enough, these utilities can also manipulate POSIX-draft ACLs so,
now there is a one stop shop for all your ACL needs.
THe NFSv4 (Network File System – Version 4) protocol introduces a new ACL (Access
Control List) format that extends other existing ACL formats. NFSv4 ACL is easy
to work with and introduces more detailed file security attributes, making NFSv4
ACLs more secure. Several operating systems like IBM® AIX®, Sun Solaris, and
Linux® have implemented NFSv4 ACL in their filesystems.
Currently, the filesystems that support NFSv4 ACL in IBM AIX 5L version 5.3
and above are NFSv4, JFS2 with EAv2 (Extended Journaled Filesystem with Extended
Attributes format version 2), and General Parallel Filesystem (GPFS). In Sun
Solaris, this ACL model is supported by ZFS. In RedHat Linux, NFSv4 supports
NFSv4 ACLs.
...ZFS supports the NFSv4 ACL model, and has implemented
the commands in the form of new options to the existing ls and chmod commands.
Thus, the ACLs can be set and displayed using the chmod and ls commands; no
new command has been introduced. Because of this, it is very easy to work with
ACLs in ZFS.
ZFS ACL format
ZFS ACLs follow a well-defined format. The format and the entities involved
in this format are:
Syntax A
ACL_entry_type:Access_permissions/…/[:Inheritance_flags]:deny or allow
|
ACL_entry_type includes "owner@", "group@", or "everyone@".
For example:
group@:write_data/append_data/execute:deny
|
Syntax B
ACL_entry_type: ACL_entry_ID:Access_permissions/…/[:Inheritance_flags]:deny or allow
|
ACL_entry_type includes "user", or "group".
ACL_entry_ID includes "user_name", or "group_name".
For example:
user:samy:list_directory/read_data/execute:allow
|
Inheritance flags
f : FILE_INHERIT
d : DIRECTORY_INHERIT
i : INHERIT_ONLY
n : NO_PROPAGATE_INHERIT
S : SUCCESSFUL_ACCESS_ACE_FLAG
F : FAILED_ACCESS_ACE_FLAG
|
Listing ACLs of ZFS files and directories
ACLs can be listed using the ls command using the -v and -V options. For
listing directory ACLs, use the -d option.
| Operation |
Command |
| Listing ACL entries of files |
ls –[v | V] <file_name> |
| Listing ACL entries of dirs |
ls –d[v | V] <dir_name> |
Example for listing ACLs of a file
ls -v file.1
-rw-r--r-- 1 root root 2703 Nov 4 12:37 file.1
0:owner@:execute:deny
1:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
2:group@:write_data/append_data/execute:deny
3:group@:read_data:allow
4:everyone@:write_data/append_data/write_xattr/execute/write_attributes/
write_acl/write_owner:deny
5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize:allow
|
Example for listing ACLs of a directory
# ls -dv dir.1
drwxr-xr-x 2 root root 2 Nov 1 14:51 dir.1
0:owner@::deny
1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory/
append_data/write_xattr/execute/write_attributes/write_acl/write_owner:allow
2:group@:add_file/write_data/add_subdirectory/append_data:deny
3:group@:list_directory/read_data/execute:allow
4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr /
write_attributes/write_acl/write_owner:deny
5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes /
read_acl/synchronize:allow
|
Example for listing ACLs in a compact format
# ls -Vd dir.1
drwxr-xr-x 2 root root 2 Sep 1 05:46 d
owner@:--------------:------:deny
owner@:rwxp---A-W-Co-:------:allow
group@:-w-p----------:------:deny
group@:r-x-----------:------:allow
everyone@:-w-p---A-W-Co-:------:deny
everyone@:r-xp--a-R-c--s:------:allow
|
In above examples, ACLs are displayed in a compact format. In this, access
permissions and inheritance flags are displayed using masks. One ACL entry is
displayed in each line, making the view easier to understand.
Modifying ACLs of ZFS files and directories
ACLs can be set or modified using the chmod command. The chmod command
uses the ACL-specification, which includes the ACL-format (Syntax
A or
B), listed earlier.
| Operation |
Command |
| Adding an ACL entry by index-ID |
# chmod Aindex_ID+acl_specification filename |
| Adding an ACL entry for a user |
# chmod A+acl_specification filename |
| Removing an ACL entry by index_ID |
# chmod Aindex_ID- filename |
| Removing an ACL entry by user |
# chmod A-acl_specification filename |
| Removing an ACL from a file |
# chmod A- filename |
| Replacing an ACL entry at index_ID |
# chmod Aindex_ID=acl_specification filename |
| Replacing an ACL of a file |
# chmod A=acl_specification filename |
Examples of ZFS ACLs modifications
List ACL entries
# ls –v a
-rw-r--r-- 1 root root 0 Sep 1 04:25 a
0:owner@:execute:deny
1:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
2:group@:write_data/append_data/execute:deny
3:group@:read_data:allow
4:everyone@:write_data/append_data/write_xattr/execute/write_attributes/
write_acl/write_owner:deny
5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize:allow
|
Add ACL entries
# chmod A+user:samy:read_data:allow a
# ls -v a
-rw-r--r--+ 1 root root 0 Sep 1 02:01 a
0:user:samy:read_data:allow
1:owner@:execute:deny
2:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
3:group@:write_data/append_data/execute:deny
4:group@:read_data:allow
5:everyone@:write_data/append_data/write_xattr/execute/write_attributes/
write_acl/write_owner:deny
6:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize:allow
# chmod A1+user:samy:execute:deny a
# ls -v a
-rw-r--r--+ 1 root root 0 Sep 1 02:01 a
0:user:samy:read_data:allow
1:user:samy:execute:deny
2:owner@:execute:deny
3:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
4:group@:write_data/append_data/execute:deny
5:group@:read_data:allow
6:everyone@:write_data/append_data/write_xattr/execute/write_attributes/
write_acl/write_owner:deny
7:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize:allow
|
Replace ACL entries
# chmod A0=user:samy:read_data/write_data:allow a
# ls -v
total 2
-rw-r--r--+ 1 root root 0 Sep 1 02:01 a
0:user:samy:read_data/write_data:allow
1:user:samy:execute:deny
2:owner@:execute:deny
3:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
4:group@:write_data/append_data/execute:deny
5:group@:read_data:allow
6:everyone@:write_data/append_data/write_xattr/execute/write_attributes/
write_acl/write_owner:deny
7:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize:allow
# chmod A=user:samy:read_data/write_data/append_data:allow a
# ls -v a
----------+ 1 root root 0 Sep 1 02:01 a
0:user:samy:read_data/write_data/append_data:allow
|
ACLs can also be modified using the masks instead of specifying complete
names.
Modifying ACL entries using masks
# ls -V a
-rw-r--r--+ 1 root root 0 Sep 5 01:50 a
user:samy:--------------:------:deny
user:samy:rwx-----------:------:allow
owner@:--x-----------:------:deny
owner@:rw-p---A-W-Co-:------:allow
group@:-wxp----------:------:deny
group@:r-------------:------:allow
everyone@:-wxp---A-W-Co-:------:deny
everyone@:r-----a-R-c--s:------:allow
# chmod A1=user:samy:rwxp:allow a
# ls -V a
-rw-r--r--+ 1 root root 0 Sep 5 01:50 a
user:samy:--------------:------:deny
user:samy:rwxp----------:------:allow
owner@:--x-----------:------:deny
owner@:rw-p---A-W-Co-:------:allow
group@:-wxp----------:------:deny
group@:r-------------:------:allow
everyone@:-wxp---A-W-Co-:------:deny
everyone@:r-----a-R-c--s:------:allow
|
Remove ACL entries
# ls -v a
-rw-r-----+ 1 root root 0 Sep 5 01:50 a
0:user:samy:read_data/write_data/execute:allow
1:owner@:execute:deny
2:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
3:group@:write_data/append_data/execute:deny
4:group@:read_data:allow
5:everyone@:read_data/write_data/append_data/write_xattr/execute/
write_attributes/write_acl/write_owner:deny
6:everyone@:read_xattr/read_attributes/read_acl/synchronize:allow
# chmod A- a
# ls -v a
-rw-r----- 1 root root 0 Sep 5 01:50 a
0:owner@:execute:deny
1:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
2:group@:write_data/append_data/execute:deny
3:group@:read_data:allow
4:everyone@:read_data/write_data/append_data/write_xattr/execute/
write_attributes/write_acl/write_owner:deny
5:everyone@:read_xattr/read_attributes/read_acl/synchronize:allow
# chmod A5- a
# ls -v a
-rw-r----- 1 root root 0 Sep 5 01:50 a
0:owner@:execute:deny
1:owner@:read_data/write_data/append_data/write_xattr/write_attributes/
write_acl/write_owner:allow
2:group@:write_data/append_data/execute:deny
3:group@:read_data:allow
4:everyone@:read_data/write_data/append_data/write_xattr/execute/
write_attributes/write_acl/write_owner:deny
|
Helps to understand the capabilities of ZFS snapshots, a read-only copy of
a Solaris ZFS file system. ZFS snapshots can be created almost instantly and
are a valuable tool for system administrators needing to perform backups.
You will learn:
- How to set up a ZFS file system
- How to use and create ZFS snapshots
- How to use ZFS snapshots for backup and restore purposes
- How to migrate ZFS snapshots between systems
After reading this guide, you will have a basic understanding of how snapshots
can be integrated into your system administration procedures.
See also
Comparison of ZFS and Linux RAID +LVM
iZFS doesn't support raid 5 but does support raid-z that has better
features and less limitations
iiRaidZ - A variation on RAID-5 which allows for better distribution
of parity and eliminates the "RAID-5 write hole" (in which data and parity become
inconsistent after a power loss). Data and parity is striped across all disks
within a raidz group. A raidz group with N disks of size X can hold approximately
(N-1)*Xbytes and can withstand one device failing before data integrity is compromised.
The minimum number of devices in a raidz group is 2; the recommended number
is between 3 and 9.
ivA clone is a writable
volume or file system whose initialcontents are the same as another dataset.
As with snapshots, creating a clone is nearly instantaneous, and initially consumes
no additional space.
v[Linux] RAID (be it hardware- or software-), assumes that if a write
to a disk doesn't return an error, then the write was successful. Therefore,
if your disk corrupts data without returning an error, your data will
become corrupted. This is of course very unlikely to happen, but it is possible,
and it would result in a corrupt filesystem. http://www.tldp.org/HOWTO/Software-RAID-HOWTO-6.html
Ashton Mills 21 June 2007327 days ago.
So, Sun's ZFS file system has garnered publicity recently with the announcement
of its inclusion in Mac OS X and, more recently, as a module for the Linux kernel.
But if you don't readFilesystems Weekly, what is it and what does it mean for
you?
Now I may just be showing my geek side a bit here, but file systems are awesome.
Aside from the fact our machines would be nothing without them, the science
behind them is frequently ingenious.
And ZFS (the Zettabyte File System) is no different. It has quite an extensive
feature set just like its peers, but builds on this by adding a new layer of
simplicity. According to the
official site, ZFS key features are (my summary):
- Pooled storage -- eliminates the concept of partitions and volumes,
everything comes from the same pool regardless of the number of physical
disks. Additionally, "combined I/O bandwidth of all devices in the pool
is available to all file systems at all times."
- All operations are copy-on-write transactions -- this is a tad
beyond me, but the key phrase here -- no need to ever fsck (chkdsk, for
you Windows people or Disk Utility repair for Mac heads) the file system.
- Disk scrubbing -- live online checking of blocks against their
checksums, and self-repair of any problems.
- Pipelined I/O -- I'll let the website explain "The pipeline operates
on I/O dependency graphs and provides scoreboarding, priority, deadline
scheduling, out-of-order issue and I/O aggregation." Or in short, it handles
loads well.
- Snapshots -- A 'read-only point-in-time copy of a filesystem',
with backups being driven using snapshots to allow, rather impressively,
not just full imaging but incremental backups from multiple snapshots. Easy
and space efficient.
- Clones -- clones are described as 'writable copies of a snapshot'
and could be used as "an extremely space-efficient way to store many copies
of mostly-shared data" which sounds rather like clones referencing snapshots
and storing only the data changed from the snapshot. On a network with imaged
desktops for eg, this would mean having only one original snapshot image,
and dozens of clones that contain only modified data, which would indeed
be extremely space efficent compared to storing dozens of snapshots.
- Built-in compression -- granted this is available for most other
filesystems, usually as an addon, and it's good point raised that compression
can not only save space, but I/O time.
- Simple administration -- one of the biggest selling points. This
is quite important because some of the above features, such as pooling,
can indirectly be achieved now with other filesystems -- layering LVM, md
RAID and Ext3 for example. However for each of these there is an entirely
different set of commands and tools to setup and administer the devices
-- what ZFS promises is that these layers can all be handled from the one
toolset, and in a simpler manner, as this
PDF tutorial demonstrates.
All up, as a geek, it's an exciting file system I'd love to play with --
currently however ZFS is part of Sun's Solaris, and under the CDDL (Common Development
and Distribution License), which is actually based on the MPL (Mozilla Public
License). As this is incompatible with the GPLv2, this means the code can't
be ported to the Linux kernel. However, this has recently been satisfied by
porting it across as a
FUSE
module but, being userspace, is slow though there hope this will improve.
Looks like it's time to enable FUSE support in my kernel!
Of course, (in a few months time) you could also go for Mac OS X where, in
Leopard, ZFS is already supported and there are rumours Apple may be preparing
to adopt it as the default filesystem replacing the aging HFS+ in the future
(but probably not in 10.5).
Description: This white paper explores the performance characteristics
and differences of ZFS in the Solaris 10 OS and the Microsoft Windows Server
2003 NTFS file system.
Jun 12, 2007
... Apple confirmed statements by Sun's Jonathan Schwartz that Leopard
will use ZFS, correcting an executive who Monday suggested otherwise.
Pawel Jakub Dawidek
pjd at FreeBSD.org
Fri Apr 6 02:58:34 UTC 2007
Hi.
I'm happy to inform that the ZFS file system is now part of the FreeBSD
operating system. ZFS is available in the HEAD branch and will be
available in FreeBSD 7.0-RELEASE as an experimental feature.
Commit log:
Please welcome ZFS - The last word in file systems.
ZFS file system was ported from OpenSolaris operating system. The code
in under CDDL license.
I'd like to thank all SUN developers that created this great piece of
software.
Supported by: Wheel LTD (http://www.wheel.pl/)
Supported by: The FreeBSD Foundation (http://www.freebsdfoundation.org/)
Supported by: Sentex (http://www.sentex.net/)
Limitations.
Currently ZFS is only compiled as kernel module and is only available
for i386 architecture. Amd64 should be available very soon, the other
archs will come later, as we implement needed atomic operations.
Missing functionality.
- We don't have iSCSI target daemon in the tree, so sharing ZVOLs via
iSCSI is also not supported at this point. This should be fixed in
the future, we may also add support for sharing ZVOLs over ggate.
- There is no support for ACLs and extended attributes.
- There is no support for booting off of ZFS file system.
Other than that, ZFS should be fully-functional.
Enjoy!
--
Pawel Jakub Dawidek http://www.wheel.pl
pjd at FreeBSD.org http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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Techworld
ZFS - the Zettabyte File System - is an enormous advance in capability on
existing file systems. It provides greater space for files, hugely improved
administration and greatly improved data security.
It is available in Sun's Solaris 10 and has been made open source. The advantages
of ZFS look so great that its use may well spread to other UNIX distributions
and even, possibly and eventually, to Windows.
Techworld has mentioned ZFS
before. Here we provide a slightly wider and more detailed look at it. If
you want to have even more information then the best resource is Sun's own
website.
Why is ZFS a good thing?
It possesses advantages compared to existing file systems in these areas:-
- Scale
- Administration
- Data security and integrity
The key area is file system administration, followed by data security and
file system size. ZFS started from a realisation that the existing file system
concepts were hardly changed at all from the early days of computing. Then a
computer knew about a disk which had files on it. A file system related to a
single disk. On today's PCs the file systems are still disk-based with the Windows
C: drive - A: and B: being floppy drives - and subsequent drives being D:, E:,
etc.
To provide more space and bandwidth a software abstraction was added between
the file system and the disks. It was called a volume manager and virtualised
several disks into a volume.
Each volume has to be administered and growing volumes and file systems takes
effort. Volume Manager software products became popular. The storage in a volume
is specific to a server and application and can't be shared. Utilisation of
storage is poor with any unused blocks on disks in volumes being unusable anywhere
else.
ZFS starts from the concept that desktop and servers have many disks and
that a good place to start abstracting this is at the operating system:file
system interface. Consequently ZFS delivers, in effect, just one volume to the
operating system. We might imagine it as disk:. From that point ZFS delivers
scale, administration and data security features that other file systems do
not.
ZFS has a layered stack with a POSIX-compliant operating system interface,
then data management functions and, below that, increasingly device-specific
functions. We might characterise ZFS as being a file system with a volume manager
included within it, the data management function.
Data security
Data protection through RAID is clever but only goes so far. When data is written
to disk it overwrites the current version of the data. There are instances of
stray or phantom writes, mis-directed writes, DMA parity errors, disk driver
bugs and accidental overwrites according to ZFS people, that the standard checksum
approach won't detect.
The checksum is stored with the data block and is valid for that data block,
but the data block shouldn't be there in the first place. The checksum is a
disk-only checksum and doesn't cover against faults in the I/O path before that
data gets written to disk.
If disks are mirrored then a block is simultaneously written to each mirror.
If one drive or controller suffers a power failure then that mirror is out of
synchronisation and needs re-synchronising with its twin.
With RAID if there is a loss of power between data and parity writes then
disk contents are corrupted.
ZFS does things differently.
First of all it uses copy-on-write technology so that existing data blocks
are not over-written. Instead new data blocks are written and their checksum
stored with the pointer to them.
When a file write has been completed then the pointers to the previous blocks
are changed so as to point to the new blocks. In other words the file write
is treated as a transaction, an event that is atomic and has to be completed
before it is confirmed or committed.
Secondly ZFS checks the disk contents looking for checksum/data mismatches.
This process is called scrubbing. Any faults are corrected and a ZFS system
exhibits what IBM calls autonomic computing capacity; it is self-healing.
Scale
ZFS uses a 128-bit addressing scheme and can store 256 quadrillion zettabytes.
A zettabyte is 2 to the power 70 bytes or a billion TB. ZFS capacity limits
are so far away as to be unimaginable. This is eye-catching stuff but unlikely
to be a factor solving 64-bit file system capacity limitations for decades.
Administration
With ZFS all storage enters a common pool, called a zpool. Every disk or array
added to ZFS disappears into this common pool. ZFS people characterise this
storage pool as being akin to a computer's virtual memory.
A hierarchy of ZFS file systems can use that pool. Each can have its own
attributes set, such as compression, a growth-limiting quota, or a set amount
of space.
I/O characteristics
ZFS has its own I/O system. I/Os have a priority with read I/Os having a higher
priority than write I/Os. That means that reads get executed even if writes
are queued up.
Write I/Os have both a priority and a deadline. The deadline is sooner the
higher the priority. Writes with the same deadline are executed in logical;
block address order so that, in effect, they form a sequential series of writes
across a disk which reduces head movement to a single sweep across the disk
surface. What's happening is that random write I/Os are getting transformed
into sets of sequential I/Os to make the overall write I/O rate faster.
Striping and blocksizes
ZFS stripes files automatically. Block sizes are dynamically set. Blocks are
allocated from disks based on an algorithm that takes into account space available
and I/O counts. When blocks are being written to the copy-on-write concept means
that a sequential set of blocks can be used, speeding up write I/O.
ZFS and NetApp's WAFL
ZFS has been based in part of NetApp's write Anywhere File Layout (WAFL) system.
It has moved on from WAFL and now has many differences. This
table lists some of them. But do read the blog replies which correct some
table errors.
There is more on the ZFS and WAFL similarities and differences
here.
Snapshots unlimited and more
ZFS can take a virtually unlimited number if snapshots and these can be used
to restore lost (deleted) files. However, they can't protect against disk crashes.
For that RAID and backup to external devices are needed.
ZFS offers compression, encryption is being developed, and an initiative
is under way to make it bootable. The compression is applied before data is
written meaning that the write I/O burden is reduced and hence effective write
speed increased further.
We may see Sun offering storage arrays with ZFS. For example we might see
a SUN NAS box based on ZFS. This is purely speculative as is the idea that we
might see Sun offered clustered NAS ZFS systems to take on Isilon and others
in the high-performance, clustered, virtualised NAS area.
So what?
There is a lot of software engineering enthusiasm for ZFS and the engineers
at Sun say that ZFS outperforms other file systems, for example the Solaris
file system. It is faster at file operations and, other things being equal,
a ZFS Solaris system will out-perform a non-ZFS Solaris system. Great, but will
it out-perform other UNIX servers and Windows servers, again with other things
being equal?
We don't know. We suspect it might but don't know by how much. Even then
the popularity of ZFS will depend upon how it is taken up by Sun Solaris 10
customers and whether ports to apple and to Linux result in wide use. For us
storage people the ports that really matter are to mainstream Unix versions
such as AIX, HP-UX and Red Hat Linux, also SuSe Linux I suppose.
There is no news of a ZFS port to Windows and Vista's own advanced file system
plans have quite recently been downgraded with its file system
changes.
If Sun storage systems using ZFS, such as its X4500 'Thumper' server, with
ZFS-enhanced direct-attached storage (DAS), and Honeycomb, become very popular
and are as market-defining as EMC's Centera product then we may well see ZFS
spreading. But their advantages have to be solid and substantial with users
getting far, far better file-based application performance and a far, far lower
storage system management burden. Such things need proving in practice.
To find out for yourself try these systems out or wait for others to do so.
How to reformat all of your systems and use ZFS.
1. So easy your mom could administer it
ZFS is administered by two commands, zpool and zfs. Most tasks typically require
a single command to accomplish. And the commands are designed to make sense.
For example, check out the commands to
create a RAID 1 mirrored filesystem and
place a quota on its size. 2. Honkin' big filesystems
How big do filesystems need to be? In a
world where 640KB is certainly not enough for computer memory, current filesystems
have reached or are reaching the end of their usefulness. A 64-bit filesystem
would meet today's need, but estimates of the lifetime of a 64-bit filesystem
is about 10 years. Extending to 128-bits gives ZFS
an expected lifetime of 30 years (UFS, for comparison, is about 20 years old).
So how much data can you squeeze into a 128-bit filesystem? 16
exabytes or 18 million terabytes. How many files can you cram into a ZFS filesystem?
200 million million.
Could anyone use a fileystem that large? No, not really.
The topic has roused discussions about
boiling the oceans if a real life storage unit that
size was powered on. It may not be necessary to have 128 bits,
but it doesn't hurt and we won't have to worry about running out of addressable
space.
3. Filesystem, heal thyself
ZFS employs 256 bit checksums end-to-end to validate data stored under its protection.
Most filesystem (and you know who you are) depend on the underlying hardware
to detect corrupt data and then can only nag about it if they get such a message.
Every block in a ZFS filesystem has a checksum associated with it. If ZFS detects
a checksum mismatch on a raidz or mirrored filesystem, it will actively reconstruct
the block from the available redundancy and go on about its job.
4. fsck off, fsck
fsck has been voted out of the house. We don't need it anymore. Because ZFS
data are always consistent on disk, don't be afraid to yank out those power
cords if you feel like it. Your ZFS filesystems will never require you to enter
the superuser password more maintenance mode.
5. Compress to your heart's content
I've always been a proponent of optional and appropriate compression in filesystems.
There are some data that are well suited to compression such as server logs.
Many people get ruffled up over this topic, although I suspect that they were
once burned by doublespace munching up an important document. When thoughtfully
used, ZFS compression can improve disk I/O which is a common bottleneck. ZFS
compression can be turned on for individual filesystems or hierarchies with
a
very easy single command.
6. Unconstrained architecture
UFS and other filesystems use a constrained model of fixed partitions or volumes,
each filesystem having a set amount of available disk space. ZFS uses a pooled
storage model. This is a significant departure from the traditional concept
of filesystems. Many current production systems may have a single digit number
of filesystems and adding or manipulating existing filesystems in such an environment
is difficult. In ZFS,
pools are created from physical storage.
Mirroring or the new
RAID-Z redundancy exists at the pool level. Instead of breaking pools apart
into filesystems, each
newly created filesystem shares the available space in the pool, although
a minimum amount of space can be
reserved for it. ZFS filesystems exist in their own hierarchy, children
filesystems inherit the properties of their parents, and each ZFS filesystem
in the ZFS hierarchy can easily be
mounted in different places in the system filesystem.
7. Grow filesystems without green thumb
If your pool becomes overcrowded, you can grow it.
With one command. On a live production system. Enough said.
8. Dynamic striping
On by default, dynamic striping automatically includes all devices in a pool
in writes simultaneously (stripe width spans all the avaiable media). This will
speed up the I/O on systems with multiple paths to storage by load balancing
the I/O on all of the paths.
9. The term "raidz" sounds so l33t
The new RAID-Z redundant storage model replaces RAID-5 and improves upon it.
RAID-Z does not suffer from the "write hole" in which a stripe of data becomes
corrupt because of a loss of power during the vulnerable period between writing
the data and the parity. RAID-Z, like RAID-5, can survive the loss of one disk.
A future release is planned using the keyword raidz2 which can tolerate the
loss of two disks. Perhaps the best feature is that
creating a raidz pool which is crazy simple.
10. Clones with no ethical issues
The simple creation of
snapshots and
clones of filesystems makes living with ZFS so much more enjoyable. A snapshot
is a read-only point-in-time copy of a filesystem which takes practically no
time to create and uses no additional space at the beginning. Any snapshot can
be cloned to make a read-write filesystem and any snapshot of a filesystem can
be
restored to the original filesystem to return to the previous state.
Snapshots can be written to other storage (disk,
tape), transferred to another system, and converted back into a filesystem.
More information
For more information, check out
Sun's
official ZFS page and the detailed
OpenSolaris
community ZFS information. If you want to take ZFS out for a test drive,
the latest version of Solaris Express has it built in and ready to go. Download
it
here.
Softpanorama Recommended
NFSv4 ACLs
WAFL
If you want to learn more about the theory behind ZFS and find reference material
have a look at ZFS Administration
Guide, OpenSolaris ZFS,
ZFS BigAdmin
and
ZFS Best Practices.
zfs-cheatsheet
ZFS
Evil Tuning Guide - Siwiki
The Musings of Chris Samuel " Blog Archive " ZFS versus XFS with Bonnie++ patched
to use random data
ZFS Tutorial Part
1
managing ZFS filesystems
For a humorous introduction to ZFS' features, see presentation given by
Pawel at EuroBSDCon 2007: http://youtube.com/watch?v=o3TGM0T1CvE.
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