This chapter provides an overview of the ZFS file system and its features and benefits. This chapter also covers some basic terminology used throughout the rest of this book.
The following sections are provided in this chapter:
This section summarizes new features in the ZFS file system.
Solaris Express Community Edition, build 129: In this Solaris release, each ZFS storage pool has an associated process, zpool-poolname. The threads in this process are the pool's I/O processing threads to handle I/O tasks, such as compression and checksumming, that are associated with the pool. The purpose of this process is to provide visibility into each storage pool's CPU utilization. Information about these process can be reviewed by using the ps and prstat commands. These processes are only available in the global zone. For more information, see sdc.1m.
Solaris Express Community Edition, build 129: In this Solaris release, you can use the deduplication property to remove redundant data from your ZFS file systems. If a file system has the dedup property enabled, duplicate data blocks are removed synchronously. The result is that only unique data is stored and common components are shared between files.
You can enable this property as follows:
# zfs set dedup=on tank/home
Although deduplication is set as a file system property, the scope is pool-wide. For example, you can identify the deduplication ratio as follows:
# zpool list tank NAME SIZE ALLOC FREE CAP DEDUP HEALTH ALTROOT tank 136G 55.2G 80.8G 40% 2.30x ONLINE -
The zpool list output has been updated to support the deduplication property. For more information, see
For more information setting the deduplication property, see The dedup Property.
For detailed information about the ZFS deduplication features, see this blog:
For up-to-date information about the ZFS deduplication features, see this FAQ:
Solaris Express Community Edition, build 128: A storage pool can become damaged if underlying devices become unavailable, a power failure occurs, or if more than the supported number of devices fail in a redundant ZFS configuration. This release provides new command features for recovering your damaged storage pool. However, using this recovery feature means that the last few transactions that occurred prior to the pool outage might be lost.
Both the zpool clear and zpool import commands support the -F option to possibly recover a damaged pool. In addition, running the zpool status, zpool clear, or zpool import command automatically report a damaged pool and these commands describe how to recover the pool.
For more information, see Repairing ZFS Storage Pool-Wide Damage.
The following log device enhancements are available in the Solaris Express Community Edition:
The logbias property – In SXCE build 122, you can use this property to provide a hint to ZFS about handling synchronous requests for a specific dataset. If logbias is set to latency, ZFS uses the pool's separate log devices, if any, to handle the requests at low latency. If logbias is set to throughput, ZFS does not use the pool's separate log devices. Instead, ZFS optimizes synchronous operations for global pool throughput and efficient use of resources. The default value is latency. For most configurations, the default value is recommended. Using the logbias=throughput value might improve performance for writing database files.
Log device removal – In SXCE build 125, you can now remove a log device from a ZFS storage pool by using the zpool remove command. A single log device can be removed by specifying the device name. A mirrored log device can be removed by specifying the top-level mirror for the log. When a separate log device is removed from the system, ZIL transaction records are written to the main pool.
Redundant top-level virtual devices are now identified with a numeric identifier. For example, in a mirrored storage pool of two disks, the top level virtual device is mirror-0.
For more information, see Example 4–3.
Solaris Express Community Edition, build 120: In this Solaris release, a redundant RAID-Z configuration can now have either single-, double-, or triple-parity, which means that one, two, three device failures can be sustained respectively, without any data loss. You can specify the raidz3 keyword for a triple-parity RAID-Z configuration. For more information, see
Solaris Express Community Edition, build 121: If you implement different automatic snapshot policies so that older snapshots are being inadvertently destroyed by zfs receive because they no longer exist on the sending side, you might consider using the snapshots hold feature in this Solaris release.
Holding a snapshot prevents it from being destroyed. In addition, this feature allows a snapshot with clones to be deleted pending the removal of the last clone by using the zfs destroy -d command.
You can hold a snapshot or set of snapshots. For example, the following syntax puts a hold tag, keep, on tank/home/cindys/snap@1.
# zfs hold keep tank/home/cindys@snap1
For more information, see Holding ZFS Snapshots.
Solaris Express Community Edition, build 117: In this Solaris release, a system event or sysevent is provided when an underlying device is expanded. ZFS has been enhanced to recognize these events and adjusts the pool based on the new size of the expanded LUN, depending on the setting of the autoexpand property. You can use the autoexpand property pool to enable or disable automatic pool expansion when a dynamic LUN expansion event is received.
These features enable you to expand a LUN and the resulting pool can access the expanded space without having to export and import pool or reboot the system.
For example, automatic LUN expansion is enabled on the tank pool.
# zpool set autoexpand=on tank
Or , you can create the pool with the autoexpand property enabled.
# zpool create -o autoexpand=on tank c1t13d0
The autoexpand property is disabled by default so you can decide whether you want the LUN expanded or not.
A LUN can also be expanded by using the zpool online -e command. For example:
# zpool online -e tank c1t6d0
Or, you can reset the autoexpand property after the LUN is attached or made available by using the zpool replace feature. For example, the following pool is created with one 8-Gbyte disk (c0t0d0). The 8-Gbyte disk is replaced with a 16-Gbyte disk (c1t13d0), but the pool size is not expanded until the autoexpand property is enabled.
# zpool create pool c0t0d0 # zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT pool 8.44G 76.5K 8.44G 0% ONLINE - # zpool replace pool c0t0d0 c1t13d0 # zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT pool 8.44G 91.5K 8.44G 0% ONLINE - # zpool set autoexpand=on pool # zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT pool 16.8G 91.5K 16.8G 0% ONLINE -
Another way to expand the LUN in the above example without enabling the autoexpand property, is to use the zpool online -e command even though the device is already online. For example:
# zpool create tank c0t0d0 # zpool list tank NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 8.44G 76.5K 8.44G 0% ONLINE - # zpool replace tank c0t0d0 c1t13d0 # zpool list tank NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 8.44G 91.5K 8.44G 0% ONLINE - # zpool online -e tank c1t13d0 # zpool list tank NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 16.8G 90K 16.8G 0% ONLINE -
Additional device replacement enhancements in this release include the following features:
In previous releases, ZFS was not able to replace an existing disk with another disk or attach a disk if the replacement disk was a slightly different size. In this release, you can replace an existing disk with another disk or attach a new disk that is nominally the same size provided that the pool is not already full.
In this release, you do not need to reboot the system or export and import a pool to expand a LUN. As described above, you can enable the autoexpand property or use the zpool online -e command to expand the full size of a LUN.
For more information about replacing devices, see Replacing Devices in a Storage Pool.
Solaris Express Community Edition, build 114: In previous Solaris releases, you could apply quotas and reservations to ZFS file systems to manage and reserve space.
In this Solaris release, you can set a quota on the amount of space consumed by files that are owned by a particular user or group. You might consider setting user and group quotas in an environment with a large number of users or groups.
You can set user or group quotas by using the zfs userquota and zfs groupquota properties as follows:
# zfs set userquota@user1=5G tank/data # zfs set groupquota@staff=10G tank/staff/admins
You can display a user's or group's current quota setting as follows:
# zfs get userquota@user1 tank/data NAME PROPERTY VALUE SOURCE tank/data userquota@user1 5G local # zfs get groupquota@staff tank/staff/admins NAME PROPERTY VALUE SOURCE tank/staff/admins groupquota@staff 10G local
Display general quota information as follows:
# zfs userspace tank/data TYPE NAME USED QUOTA POSIX User root 3K none POSIX User user1 0 5G
# zfs groupspace tank/staff/admins TYPE NAME USED QUOTA POSIX Group root 3K none POSIX Group staff 0 10G
You can display individual user or group space usage by viewing the userused@user and groupused@group properties as follows:
# zfs get userused@user1 tank/staff NAME PROPERTY VALUE SOURCE tank/staff userused@user1 213M local # zfs get groupused@staff tank/staff NAME PROPERTY VALUE SOURCE tank/staff groupused@staff 213M local
For more information about setting user quotas, see Setting ZFS Quotas and Reservations.
Solaris Express Community Edition, build 103: In previous Solaris releases, you could apply ACL inheritance so that all files are created with 0664 or 0666 permissions. If you want to optionally include the execute bit from the file creation mode into the inherited ACL, you can use the pass through inheritance for execute permission in this release.
If aclinherit=passthrough-x is enabled on a ZFS dataset, you can include execute permission for an output file that is generated from cc or gcc tools. If the inherited ACL does not include execute permission, then the executable output from the compiler won't be executable until you use the chmod command to change the file's permissions.
For more information, see Example 8–13.
Solaris Express Community Edition, build 100: This release includes the Time Slider snapshot tool. This tool automatically snapshots ZFS file systems and allows you to browse and recover snapshots of file systems. For more information, see Managing Automatic ZFS Snapshots.
Solaris Express Community Edition, builds 96-128: The following ZFS file system enhancements are included in these releases.
Setting ZFS Security Labels – The mlslabel property is a sensitivity label that determines if a dataset can be mounted in a Trusted Extensions labeled-zone. The default is none. The mlslabel property can be modified only when Trusted Extensions is enabled and only with the appropriate privilege.
Setting ZFS file system properties at pool creation time – You can set ZFS file system properties when the pool is created. In the following example, compression is enabled on the ZFS file system that is created when the pool is created.
# zpool create -O compression=on pool mirror c0t1d0 c0t2d0
Setting cache properties on a ZFS file system – Two new ZFS file system properties are provided in that allow you to control what is cached in the primary cache (ARC) or the secondary cache (L2ARC). The cache properties are set as follows:
primarycache – Controls what is cached in the ARC.
secondarycache – Controls what is cached in the L2ARC.
Possible values for both properties – all, none, and metadata. If set to all, both user data and metadata are cached. If set to none, neither user data nor metadata is cached. If set to metadata, only metadata is cached. The default is all.
You can set these properties on an existing file system or when the file system is created. For example:
# zfs set primarycache=metadata tank/datab # zfs create -o primarycache=metadata tank/newdatab
When set on existing file systems, only new I/O is cache based on the value of these properties.
Some database environments might benefit from not caching user data. You will have determine if setting cache properties is appropriate for your environment.
Space accounting properties – New read-only file system properties help you identify space usage for clones, file systems, and volumes, but not snapshots. The properties are as follows:
usedbychildren – Identifies the amount of space that is used by children of this dataset, which would be freed if all the dataset's children were destroyed. The property abbreviation is usedchild.
usedbydataset – Identifies the amount of space that is used by this dataset itself, which would be freed if the dataset was destroyed, after first destroying any snapshots and removing any refreservation. The property abbreviation is usedds.
usedbyrefreservation – Identifies the amount of space that is used by a refreservation set on this dataset, which would be freed if the refreservation was removed. The property abbreviation is usedrefreserv.
usedbysnapshots – Identifies the amount of space that is consumed by snapshots of this dataset. In particular, it is the amount of space that would be freed if all of this dataset's snapshots were destroyed. Note that this is not simply the sum of the snapshots' used properties, because space can be shared by multiple snapshots. The property abbreviation is usedsnap.
These new properties break down the value of the used property into the various elements that consume space. In particular, the value of the used property breaks down as follows:
used property = usedbychildren + usedbydataset + usedbyrefreservation + usedbysnapshots
You can view these properties by using the zfs list -o space command. For example:
$ zfs list -o space NAME AVAIL USED USEDSNAP USEDDS USEDREFRESERV USEDCHILD rpool 25.4G 7.79G 0 64K 0 7.79G rpool/ROOT 25.4G 6.29G 0 18K 0 6.29G rpool/ROOT/snv_98 25.4G 6.29G 0 6.29G 0 0 rpool/dump 25.4G 1.00G 0 1.00G 0 0 rpool/export 25.4G 38K 0 20K 0 18K rpool/export/home 25.4G 18K 0 18K 0 0 rpool/swap 25.8G 512M 0 111M 401M 0
The above command is equivalent to the zfs list -o name,avail,used,usedsnap,usedds,usedrefreserv,usedchild -t filesystem,volume command.
Listing snapshots – The listsnapshots pool property controls whether snapshot information is displayed by the zfs list command. The default value is off, which means snapshot information is not displayed by default.
You can use the zfs list -t snapshots command to display snapshot information. For example:
# zfs list -t snapshot NAME USED AVAIL REFER MOUNTPOINT pool/home@today 16K - 22K - pool/home/user1@today 0 - 18K - pool/home/user2@today 0 - 18K - pool/home/user3@today 0 - 18K -
To display snapshot information by default, set the listsnapshots property. For example:
# zpool get listsnapshots pool NAME PROPERTY VALUE SOURCE pool listsnapshots off default # zpool set listsnaps=on pool # zfs list NAME USED AVAIL REFER MOUNTPOINT pool 208K 6.71G 19K /pool pool/home 92K 6.71G 22K /pool/home pool/home@today 16K - 22K - pool/home/user1 18K 6.71G 18K /pool/home/user1 pool/home/user1@today 0 - 18K - pool/home/user2 18K 6.71G 18K /pool/home/user2 pool/home/user2@today 0 - 18K - pool/home/user3 18K 6.71G 18K /pool/home/user3 pool/home/user3@today 0 - 18K -
Keep in mind that changing the default listsnapshots setting might cause the zfs list output to run slowly in a pool with many snapshots.
Solaris Express Community Edition, build 96: In this release, ZFS identifies intent log failures in the zpool status command. FMA reports these errors as well. Both ZFS and FMA describe how to recover from an intent log failure.
For example, if the system shuts down abruptly before synchronous write operations are committed to a pool with a separate log device, you will see messages similar to the following:
# zpool status -x pool: pool state: FAULTED status: One or more of the intent logs could not be read. Waiting for adminstrator intervention to fix the faulted pool. action: Either restore the affected device(s) and run 'zpool online', or ignore the intent log records by running 'zpool clear'. scrub: none requested config: NAME STATE READ WRITE CKSUM pool FAULTED 0 0 0 bad intent log mirror ONLINE 0 0 0 c0t1d0 ONLINE 0 0 0 c0t4d0 ONLINE 0 0 0 logs FAULTED 0 0 0 bad intent log c0t5d0 UNAVAIL 0 0 0 cannot open
You will need to resolve the log device failure in the following ways:
Replace or recover the log device. In this example, the device c0t5d0.
Bring the log device back online.
# zpool online pool c0t5d0
Reset the failed log device error condition.
# zpool clear pool
If you want to recover from this error without replacing log device failure, you can clear the error with the zpool clear command. In this scenario, the pool will operate in degraded mode and the log records will be written to the main pool until the separate log device is replaced.
Consider using mirrored log devices to reduce the log device failure scenario.
Solaris Express Community Edition, build 95: This release provides the ability to apply NFSv4–style ACLs in sets, rather than apply different ACL permissions individually. The following ACL sets are provided:
full_set = all permissions
modify_set = all permissions except write_acl and write_owner
read_set = read_data, read_attributes, read_xattr, and read_acl
write_set = write_data, append_data, write_attributes, and write_xattr
These ACL sets are prefined and cannot be modified.
For more information about using ACL sets, see Example 8–5.
Solaris Express Community Edition, build 78: In this Solaris release, you can create pool and specify cache devices, which are used to cache storage pool data.
Cache devices provide an additional layer of caching between main memory and disk. Using cache devices provide the greatest performance improvement for random read-workloads of mostly static content.
One or more cache devices can specified when the pool is created. For example:
# zpool create pool mirror c0t2d0 c0t4d0 cache c0t0d0 # zpool status pool pool: pool state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM pool ONLINE 0 0 0 mirror ONLINE 0 0 0 c0t2d0 ONLINE 0 0 0 c0t4d0 ONLINE 0 0 0 cache c0t0d0 ONLINE 0 0 0 errors: No known data errors
After cache devices are added, they gradually fill with content from main memory. Depending on the size of your cache device, it could take over an hour for them to fill. Capacity and reads can be monitored by using the zpool iostat command as follows:
# zpool iostat -v pool 5
Cache devices can be added or removed from the pool after the pool is created.
Solaris Express Community Edition, build 90: This release provides the ability to install and boot a ZFS root file system. You can use the initial installation option or the JumpStart feature to install a ZFS root file system. Or, you can use the Live Upgrade feature to migrate a UFS root file system to a ZFS root file system. ZFS support for swap and dump devices is also provided. For more information, see Chapter 5, Installing and Booting a ZFS Root File System.
For a list of known issues with this release, go to the following site:
Solaris Express Community Edition, build 80: This release provides the ability to rollback a dataset without unmounting it first. This feature means that zfs rollback -f option is no longer needed to force an umount operation. The -f option is no longer supported, and is ignored if specified.
Solaris Express Community Edition, build 77: This release includes the following enhancements to the zfs send command.
Send all incremental streams from one snapshot to a cumulative snapshot. For example:
# zfs list NAME USED AVAIL REFER MOUNTPOINT pool 428K 16.5G 20K /pool pool/fs 71K 16.5G 21K /pool/fs pool/fs@snapA 16K - 18.5K - pool/fs@snapB 17K - 20K - pool/fs@snapC 17K - 20.5K - pool/fs@snapD 0 - 21K - # zfs send -I pool/fs@snapA pool/fs@snapD > /snaps/fs@combo
Send all incremental snapshots between fs@snapA to fs@snapD to fs@combo.
Send an incremental stream from the origin snapshot to create a clone. The original snapshot must already exist on the receiving side to accept the incremental stream. For example:
# zfs send -I pool/fs@snap1 pool/clone@snapA > /snaps/fsclonesnap-I . . # zfs receive -F pool/clone < /snaps/fsclonesnap-I
Send a replication stream of all descendent file systems, up to the named snapshots. When received, all properties, snapshots, descendent file systems, and clones are preserved. For example:
zfs send -R pool/fs@snap > snaps/fs-R
For an extended example, see Example 7–1.
Send an incremental replication stream.
zfs send -R -[iI] @snapA pool/fs@snapD
For an extended example, see Example 7–1.
For more information, see Sending and Receiving Complex ZFS Snapshot Streams.
Solaris Express Community Edition, build 77: In addition to the existing ZFS quota and reservation features, this release includes dataset quotas and reservations that do not include descendents, such as snapshots and clones, in the space consumption accounting.
The refquota property limits the amount of space a dataset can consume. This property enforces a hard limit on the amount of space that can be used. This hard limit does not include space used by descendents, such as snapshots and clones.
The refreservation property sets the minimum amount of space that is guaranteed to a dataset, not including its descendents.
For example, you can set a 10 Gbyte refquota for studentA that sets a 10-Gbyte hard limit of referenced space. For additional flexibility, you can set a 20-Gbyte quota that allows you to manage studentA's snapshots.
# zfs set refquota=10g tank/studentA # zfs set quota=20g tank/studentA
For more information, see Setting ZFS Quotas and Reservations.
Solaris Express Community Edition, build 77: This release provides support for the SolarisTM Common Internet File System (CIFS) service. This product provides the ability to share files between Solaris and Windows or MacOS systems.
To facilitate sharing files between these systems by using the Solaris CIFS service, the following new ZFS properties are provided:
Case sensitivity support (casesensitivity)
Non-blocking mandatory locks (nbmand)
SMB share support (sharesmb)
Unicode normalization support (normalization)
UTF-8 character set support (utf8only)
Currently, the sharesmb property is available to share ZFS files in the Solaris CIFS environment. More ZFS CIFS-related properties will be available in an upcoming release. For information about using the sharesmb property, see Sharing ZFS Files in a Solaris CIFS Environment.
In addition to the ZFS properties added for supporting the Solaris CIFS software product, the vscan property is available for scanning ZFS files if you have a 3rd-party virus scanning engine.
Solaris Express Community Edition, build 77: ZFS storage pool properties were introduced in an earlier release. This release provides for additional property information. For example:
# zpool get all mpool NAME PROPERTY VALUE SOURCE mpool size 33.8G - mpool used 5.76G - mpool available 28.0G - mpool capacity 17% - mpool altroot - default mpool health ONLINE - mpool guid 2689713858991441653 - mpool version 10 default mpool bootfs mpool/ROOT/zfsBE local mpool delegation on default mpool autoreplace off default mpool cachefile - default mpool failmode continue local
For a description of these properties, see Table 4–1.
The cachefile property – Solaris Express Community Edition, build 77: This release provides the cachefile property, which controls where pool configuration information is cached. All pools in the cache are automatically imported when the system boots. However, installation and clustering environments might need to cache this information in a different location so that pools are not automatically imported.
You can set this property to cache pool configuration in a different location that can be imported later by using the zpool import c command. For most ZFS configurations, this property would not be used.
The cachefile property is not persistent and is not stored on disk. This property replaces the temporary property that was used to indicate that pool information should not be cached in previous Solaris releases.
The failmode property – Solaris Express Community Edition, build 77: This release provides the failmode property for determining the behavior of a catastrophic pool failure due to a loss of device connectivity or the failure of all devices in the pool. The failmode property can be set to these values: wait, continue, or panic. The default value is wait, which means you must reconnect the device or replace a failed device and clear the error with the zpool clear command.
The failmode property is set like other settable ZFS properties, which can be set either before or after the pool is created. For example:
# zpool set failmode=continue tank # zpool get failmode tank NAME PROPERTY VALUE SOURCE tank failmode continue local
# zpool create -o failmode=continue users mirror c0t1d0 c1t1d0
For a description of all ZFS pool properties, see Table 4–1.
When file systems are created on the NFS server, the NFS client can automatically discover these newly created file systems within their existing mount of a parent file system.
For example, if the server neo already shares the tank file system and client zee has it mounted, /tank/baz is automatically visible on the client after it is created on the server.
zee# mount neo:/tank /mnt zee# ls /mnt baa bar neo# zfs create tank/baz zee% ls /mnt baa bar baz zee% ls /mnt/baz file1 file2
Solaris Express Community Edition, build 69: The zpool history command has been enhanced to provide the following new features:
ZFS file system event information is displayed. For example:
# zpool history History for 'rpool': 2009-08-26.16:49:07 zpool create -f -o failmode=continue -R /a -m legacy -o cachefile= /tmp/root/etc/zfs/zpool.cache rpool c1t1d0s0 2009-08-26.16:49:08 zfs set canmount=noauto rpool 2009-08-26.16:49:08 zfs set mountpoint=/rpool rpool 2009-08-26.16:49:09 zfs create -o mountpoint=legacy rpool/ROOT 2009-08-26.16:49:10 zfs create -b 8192 -V 2048m rpool/swap 2009-08-26.16:49:11 zfs create -b 131072 -V 1024m rpool/dump 2009-08-26.16:49:14 zfs create -o canmount=noauto rpool/ROOT/zfs1009BE 2009-08-26.16:49:15 zpool set bootfs=rpool/ROOT/zfs1009BE rpool 2009-08-26.16:49:15 zfs set mountpoint=/ rpool/ROOT/zfs1009BE 2009-08-26.16:49:16 zfs set canmount=on rpool 2009-08-26.16:49:17 zfs create -o mountpoint=/export rpool/export 2009-08-26.16:49:18 zfs create rpool/export/home 2009-08-28.08:17:59 zpool attach rpool c1t1d0s0 c1t0d0s0
A -l option for displaying a long format that includes the user name, the hostname, and the zone in which the operation was performed. For example:
# zpool history -l rpool History for 'rpool': 2009-08-26.16:49:07 zpool create -f -o failmode=continue -R /a -m legacy -o cachefile= /tmp/root/etc/zfs/zpool.cache rpool c1t1d0s0 [user root on neo:global] 2009-08-26.16:49:08 zfs set canmount=noauto rpool [user root on neo:global] 2009-08-26.16:49:08 zfs set mountpoint=/rpool rpool [user root on neo:global] 2009-08-26.16:49:09 zfs create -o mountpoint=legacy rpool/ROOT [user root on neo:global] 2009-08-26.16:49:10 zfs create -b 8192 -V 2048m rpool/swap [user root on neo:global] 2009-08-26.16:49:11 zfs create -b 131072 -V 1024m rpool/dump [user root on neo:global] 2009-08-26.16:49:14 zfs create -o canmount=noauto rpool/ROOT/zfs1009BE [user root on neo:global] 2009-08-26.16:49:15 zpool set bootfs=rpool/ROOT/zfs1009BE rpool [user root on neo:global] 2009-08-26.16:49:15 zfs set mountpoint=/ rpool/ROOT/zfs1009BE [user root on neo:global] 2009-08-26.16:49:16 zfs set canmount=on rpool [user root on neo:global] 2009-08-26.16:49:17 zfs create -o mountpoint=/export rpool/export [user root on neo:global] 2009-08-26.16:49:18 zfs create rpool/export/home [user root on neo:global] 2009-08-28.08:17:59 zpool attach rpool c1t1d0s0 c1t0d0s0 [user root on neo:global]
A -i option for displaying internal event information that can be used for diagnostic purposes. For example:
# zpool history -i rpool History for 'rpool': 2009-08-26.16:49:07 zpool create -f -o failmode=continue -R /a -m legacy -o cachefile= /tmp/root/etc/zfs/zpool.cache rpool c1t1d0s0 2009-08-26.16:49:07 [internal property set txg:6] mountpoint=/ dataset = 16 2009-08-26.16:49:07 [internal property set txg:7] mountpoint=legacy dataset = 16 2009-08-26.16:49:08 [internal property set txg:8] canmount=2 dataset = 16 2009-08-26.16:49:08 zfs set canmount=noauto rpool 2009-08-26.16:49:08 [internal property set txg:10] mountpoint=/rpool dataset = 16 2009-08-26.16:49:08 zfs set mountpoint=/rpool rpool 2009-08-26.16:49:09 [internal create txg:12] dataset = 31 2009-08-26.16:49:09 [internal property set txg:13] mountpoint=legacy dataset = 31 2009-08-26.16:49:09 zfs create -o mountpoint=legacy rpool/ROOT 2009-08-26.16:49:09 [internal create txg:15] dataset = 37 2009-08-26.16:49:10 [internal property set txg:16] refreservation=2147483648 dataset = 37 2009-08-26.16:49:10 [internal refreservation set txg:16] 2147483648 dataset = 37 2009-08-26.16:49:10 zfs create -b 8192 -V 2048m rpool/swap 2009-08-26.16:49:10 [internal create txg:18] dataset = 43 2009-08-26.16:49:10 [internal property set txg:19] refreservation=1073741824 dataset = 43 2009-08-26.16:49:10 [internal refreservation set txg:19] 1073741824 dataset = 43 . . .
For more information about using the zpool history command, see Identifying Problems in ZFS.
Solaris Express Community Edition, build 69: The zfs upgrade command is included in this release to provide future ZFS file system enhancements to existing file systems. ZFS storage pools have a similar upgrade feature to provide pool enhancements to existing storage pools.
# zfs upgrade This system is currently running ZFS filesystem version 3. All filesystems are formatted with the current version.
File systems that are upgraded and any streams created from those upgraded file systems by the zfs send command are not accessible on systems that are running older software releases.
Solaris Express Community Edition, build 69: In this release, you can delegate fine-grained permissions to perform ZFS administration tasks to non-privileged users.
You can use the zfs allow and zfs unallow commands to grant and remove permissions.
You can modify the ability to use delegated administration with the pool's delegation property. For example:
# zpool get delegation users NAME PROPERTY VALUE SOURCE users delegation on default # zpool set delegation=off users # zpool get delegation users NAME PROPERTY VALUE SOURCE users delegation off local
By default, the delegation property is enabled.
Solaris Express Community Edition, build 68: The ZFS intent log (ZIL) is provided to satisfy POSIX requirements for synchronous transactions. For example, databases often require their transactions to be on stable storage devices when returning from a system call. NFS and other applications can also use fsync() to ensure data stability. By default, the ZIL is allocated from blocks within the main storage pool. However, better performance might be possible by using separate intent log devices in your ZFS storage pool, such as with NVRAM or a dedicated disk.
Log devices for the ZFS intent log are not related to database log files.
You can set up a ZFS logging device when the storage pool is created or after the pool is created. For examples of setting up log devices, see Creating a ZFS Storage Pool with Log Devices and Adding Devices to a Storage Pool.
You can attach a log device to an existing log device to create a mirrored log device. This operation is identical to attaching a device in a unmirrored storage pool.
Consider the following points when determining whether setting up a ZFS log device is appropriate for your environment:
Any performance improvement seen by implementing a separate log device depends on the device type, the hardware configuration of the pool, and the application workload. For preliminary performance information, see this blog:
Log devices can be unreplicated or mirrored, but RAID-Z is not supported for log devices.
If a separate log device is not mirrored and the device that contains the log fails, storing log blocks reverts to the storage pool.
Log devices can be added, replaced, attached, detached, and imported and exported as part of the larger storage pool. Currently, log devices cannot be removed.
The minimum size of a log device is the same as the minimum size of each device in a pool, which is 64 Mbytes. The amount of in-play data that might be stored on a log device is relatively small. Log blocks are freed when the log transaction (system call) is committed.
The maximum size of a log device should be approximately 1/2 the size of physical memory because that is the maximum amount of potential in-play data that can be stored. For example, if a system has 16 Gbytes of physical memory, consider a maximum log device size of 8 Gbytes.
Solaris Express Community Edition, build 68: You can use the -p option with the zfs create, zfs clone, and zfs rename commands to quickly create a non-existent intermediate dataset, if it doesn't already exist.
For example, create ZFS datasets (users/area51) in the datab storage pool.
# zfs list NAME USED AVAIL REFER MOUNTPOINT datab 106K 16.5G 18K /datab # zfs create -p -o compression=on datab/users/area51
If the intermediate dataset exists during the create operation, the operation completes successfully.
Properties specified apply to the target dataset, not to the intermediate datasets. For example:
# zfs get mountpoint,compression datab/users/area51 NAME PROPERTY VALUE SOURCE datab/users/area51 mountpoint /datab/users/area51 default datab/users/area51 compression on local
The intermediate dataset is created with the default mount point. Any additional properties are disabled for the intermediate dataset. For example:
# zfs get mountpoint,compression datab/users NAME PROPERTY VALUE SOURCE datab/users mountpoint /datab/users default datab/users compression off default
For more information, see zfs(1M).
Solaris Express Community Edition, build 68: In this release, ZFS more effectively responds to devices that are removed and provides a mechanism to automatically identify devices that are inserted with the following enhancements:
You can replace an existing device with an equivalent device without having to use the zpool replace command.
The autoreplace property controls automatic device replacement. If set to off, device replacement must be initiated by the administrator by using the zpool replace command. If set to on, any new device, found in the same physical location as a device that previously belonged to the pool, is automatically formatted and replaced. The default behavior is off.
The storage pool state REMOVED is provided when a device or hot spare has been removed if the device was physically removed while the system was running. A hot-spare device is substituted for the removed device, if available.
If a device is removed and then inserted, the device is placed online. If a hot-spare was activated when the device is re-inserted, the spare is removed when the online operation completes.
Automatic detection when devices are removed or inserted is hardware-dependent and might not be supported on all platforms. For example, USB devices are automatically configured upon insertion. However, you might have to use the cfgadm -c configure command to configure a SATA drive.
Hot spares are checked periodically to make sure they are online and available.
For more information, see zpool(1M).
Solaris Express Community Edition, build 63: You can recursively rename all descendent ZFS snapshots by using the zfs rename -r command.
For example, snapshot a set of ZFS file systems.
# zfs snapshot -r users/home@today # zfs list NAME USED AVAIL REFER MOUNTPOINT users 216K 16.5G 20K /users users/home 76K 16.5G 22K /users/home users/home@today 0 - 22K - users/home/markm 18K 16.5G 18K /users/home/markm users/home/markm@today 0 - 18K - users/home/marks 18K 16.5G 18K /users/home/marks users/home/marks@today 0 - 18K - users/home/neil 18K 16.5G 18K /users/home/neil users/home/neil@today 0 - 18K -
Then, rename the snapshots the following day.
# zfs rename -r users/home@today @yesterday # zfs list NAME USED AVAIL REFER MOUNTPOINT users 216K 16.5G 20K /users users/home 76K 16.5G 22K /users/home users/home@yesterday 0 - 22K - users/home/markm 18K 16.5G 18K /users/home/markm users/home/markm@yesterday 0 - 18K - users/home/marks 18K 16.5G 18K /users/home/marks users/home/marks@yesterday 0 - 18K - users/home/neil 18K 16.5G 18K /users/home/neil users/home/neil@yesterday 0 - 18K -
Snapshots are the only dataset that can be renamed recursively.
For more information about snapshots, see Overview of ZFS Snapshots and this blog entry that describes how to create rolling snapshots:
Solaris Express Community Edition, build 62: In this Solaris release, support for booting a ZFS file system is available on x86 systems. For more information, see:
Solaris Express Community Edition, build 62: In this Solaris release, you can set gzip compression on ZFS file systems in addition to lzjb compression. You can specify compression as gzip, the default, or gzip-N, where N equals 1 through 9. For example:
# zfs create -o compression=gzip users/home/snapshots # zfs get compression users/home/snapshots NAME PROPERTY VALUE SOURCE users/home/snapshots compression gzip local # zfs create -o compression=gzip-9 users/home/oldfiles # zfs get compression users/home/oldfiles NAME PROPERTY VALUE SOURCE users/home/oldfiles compression gzip-9 local
For more information about setting ZFS properties, see Setting ZFS Properties.
Solaris Express Community Edition, build 61: As a reliability feature, ZFS file system metadata is automatically stored multiple times across different disks, if possible. This feature is known as ditto blocks.
In this Solaris release, you can specify that multiple copies of user data is also stored per file system by using the zfs set copies command. For example:
# zfs set copies=2 users/home # zfs get copies users/home NAME PROPERTY VALUE SOURCE users/home copies 2 local
Available values are 1, 2, or 3. The default value is 1. These copies are in addition to any pool-level redundancy, such as in a mirrored or RAID-Z configuration.
The benefits of storing multiple copies of ZFS user data are as follows:
Improves data retention by allowing recovery from unrecoverable block read faults, such as media faults (bit rot) for all ZFS configurations.
Provides data protection even in the case where only a single disk is available.
Allows you to select data protection policies on a per-file system basis, beyond the capabilities of the storage pool.
Depending on the allocation of the ditto blocks in the storage pool, multiple copies might be placed on a single disk. A subsequent full disk failure might cause all ditto blocks to be unavailable.
You might consider using ditto blocks when you accidentally create a non-redundant pool and when you need to set data retention policies.
For a detailed description of how setting copies on a system with a single-disk pool or a multiple-disk pool might impact overall data protection, see this blog:
For more information about setting ZFS properties, see Setting ZFS Properties.
Solaris Express Community Edition, build 57: You can use the zpool status -v command to display a list of files with persistent errors. Previously, you had to use the find -inum command to identify the filenames from the list of displayed inodes.
For more information about displaying a list of files with persistent errors, see Repairing a Corrupted File or Directory.
Solaris Express Community Release, build 54: In this Solaris release, you can create a ZFS volume as a Solaris iSCSI target device by setting the shareiscsi property on the ZFS volume. This method is a convenient way to quickly set up a Solaris iSCSI target. For example:
# zfs create -V 2g tank/volumes/v2 # zfs set shareiscsi=on tank/volumes/v2 # iscsitadm list target Target: tank/volumes/v2 iSCSI Name: iqn.1986-03.com.sun:02:984fe301-c412-ccc1-cc80-cf9a72aa062a Connections: 0
After the iSCSI target is created, set up the iSCSI initiator. For information about setting up a Solaris iSCSI initiator, see Chapter 14, Configuring Solaris iSCSI Targets and Initiators (Tasks), in System Administration Guide: Devices and File Systems.
For more information about managing a ZFS volume as an iSCSI target, see Using a ZFS Volume as a Solaris iSCSI Target.
Solaris Express Community Release, build 53: In this Solaris release, the process of sharing file systems has been improved. Although modifying system configuration files, such as /etc/dfs/dfstab, is unnecessary for sharing ZFS file systems, you can use the sharemgr command to manage ZFS share properties. The sharemgr command enables you to set and manage share properties on share groups. ZFS shares are automatically designated in the zfs share group.
As in previous releases, you can set the ZFS sharenfs property on a ZFS file system to share a ZFS file system. For example:
# zfs set sharenfs=on tank/home
Or, you can use the new sharemgr add-share subcommand to share a ZFS file system in the zfs share group. For example:
# sharemgr add-share -s tank/data zfs # sharemgr show -vp zfs zfs nfs=() zfs/tank/data /tank/data /tank/data/1 /tank/data/2 /tank/data/3
Then, you can use the sharemgr command to manage ZFS shares. The following example shows how to use sharemgr to set the nosuid property on the shared ZFS file systems. You must preface ZFS share paths with a /zfs designation.
# sharemgr set -P nfs -p nosuid=true zfs/tank/data # sharemgr show -vp zfs zfs nfs=() zfs/tank/data nfs=(nosuid="true") /tank/data /tank/data/1 /tank/data/2 /tank/data/3
For more information, see sharemgr(1M).
# zpool history History for 'newpool': 2007-04-25.11:37:31 zpool create newpool mirror c0t8d0 c0t10d0 2007-04-25.11:37:46 zpool replace newpool c0t10d0 c0t9d0 2007-04-25.11:38:04 zpool attach newpool c0t9d0 c0t11d0 2007-04-25.11:38:09 zfs create newpool/user1 2007-04-25.11:38:15 zfs destroy newpool/user1 History for 'tank': 2007-04-25.11:46:28 zpool create tank mirror c1t0d0 c2t0d0 mirror c3t0d0 c4t0d0
This features enables you or Sun support personnel to identify the exact set of ZFS commands that was executed to troubleshoot an error scenario.
You can identify a specific storage pool with the zpool history command. For example:
# zpool history newpool History for 'newpool': 2007-04-25.11:37:31 zpool create newpool mirror c0t8d0 c0t10d0 2007-04-25.11:37:46 zpool replace newpool c0t10d0 c0t9d0 2007-04-25.11:38:04 zpool attach newpool c0t9d0 c0t11d0 2007-04-25.11:38:09 zfs create newpool/user1 2007-04-25.11:38:15 zfs destroy newpool/user1
In this Solaris release, the zpool history command does not record user-ID, hostname, or zone-name. For more information, see ZFS Command History Enhancements (zpool history).
For more information about troubleshooting ZFS problems, see Identifying Problems in ZFS.
Solaris Express Community Release, build 56: You can use the xattr property to disable or enable extended attributes for a specific ZFS file system. The default value is on. For a description of ZFS properties, see Introducing ZFS Properties.
Solaris Express Community Release, build 48: The new canmount property allows you to specify whether a dataset can be mounted by using the zfs mount command. For more information, see The canmount Property.
Solaris Express Community Release, build 48: In addition to the standard native properties that can either export internal statistics or control ZFS file system behavior, ZFS supports user properties. User properties have no effect on ZFS behavior, but you can use them to annotate datasets with information that is meaningful in your environment.
For more information, see ZFS User Properties.
Solaris Express Community Release, build 48: In this Solaris release, you can set properties when you create a file system, in addition to setting properties after the file system is created.
The following examples illustrate equivalent syntax:
# zfs create tank/home # zfs set mountpoint=/export/zfs tank/home # zfs set sharenfs=on tank/home # zfs set compression=on tank/home
# zfs create -o mountpoint=/export/zfs -o sharenfs=on -o compression=on tank/home
Solaris Express Community Release, build 48: In this Solaris release, you can use various forms of the zfs get command to display information about all datasets if you do not specify a dataset or if you do not specify all. In previous releases, all dataset information was not retreivable with the zfs get command.
# zfs get -s local all tank/home atime off local tank/home/bonwick atime off local tank/home/marks quota 50G local
Solaris Express Community Release, build 48: In this Solaris release, you can use the new -F option to the zfs receive command to force a rollback of the file system to the most recent snapshot before doing the receive. Using this option might be necessary when the file system is modified between the time a rollback occurs and the receive is initiated.
For more information, see Receiving a ZFS Snapshot.
Solaris Express Community Release, build 43: When you use the zfs snapshot command to create a file system snapshot, you can use the -r option to recursively create snapshots for all descendent file systems. In addition, using the -r option recursively destroys all descendent snapshots when a snapshot is destroyed.
Recursive ZFS snapshots are created quickly as one atomic operation. The snapshots are created together (all at once) or not created at all. The benefit of atomic snapshots operations is that the snapshot data is always taken at one consistent time, even across descendent file systems.
For more information, see Creating and Destroying ZFS Snapshots.
Solaris Express Community Release, build 42: A redundant RAID-Z configuration can now have either single- or double-parity, which means that one or two device failures can be sustained respectively, without any data loss. You can specify the raidz2 keyword for a double-parity RAID-Z configuration. Or, you can specify the raidz or raidz1 keyword for a single-parity RAID-Z configuration.
Solaris Express Community Release, build 42: The ZFS hot spares feature enables you to identify disks that could be used to replace a failed or faulted device in one or more storage pools. Designating a device as a hot spare means that if an active device in the pool fails, the hot spare automatically replaces the failed device. Or, you can manually replace a device in a storage pool with a hot spare.
Solaris Express Community Release, build 42: The zfs promote command enables you to replace an existing ZFS file system with a clone of that file system. This feature is helpful when you want to run tests on an alternative version of a file system and then, make that alternative version of the file system the active file system.
Solaris Express Community Release, build 39: You can upgrade your storage pools to a newer version to take advantage of the latest features by using the zpool upgrade command. In addition, the zpool status command has been modified to notify you when your pools are running older versions.
If you want to use the ZFS Administration console on a system with a pool from a previous Solaris release, make sure you upgrade your pools before using the ZFS Administration console. To see if your pools need to be upgraded, use the zpool status command. For information about the ZFS Administration console, see ZFS Web-Based Management.
Solaris Express Community Release, build 39: When the source zonepath and the target zonepath both reside on ZFS and are in the same pool, zoneadm clone now automatically uses the ZFS clone feature to clone a zone. This enhancement means that zoneadm clone will take a ZFS snapshot of the source zonepath and set up the target zonepath. The snapshot is named SUNWzoneX, where X is a unique ID used to distinguish between multiple snapshots. The destination zone's zonepath is used to name the ZFS clone. A software inventory is performed so that a snapshot used at a future time can be validated by the system. Note that you can still specify that the ZFS zonepath be copied instead of the ZFS clone, if desired.
To clone a source zone multiple times, a new parameter added to zoneadm allows you to specify that an existing snapshot should be used. The system validates that the existing snapshot is usable on the target. Additionally, the zone install process now has the capability to detect when a ZFS file system can be created for a zone, and the uninstall process can detect when a ZFS file system in a zone can be destroyed. These steps are then performed automatically by the zoneadm command.
Keep the following points in mind when using ZFS on a system with Solaris containers installed:
Do not use the ZFS snapshot features to clone a zone
For more information, see System Administration Guide: Virtualization Using the Solaris Operating System.
Solaris Express Community Release, build 38: In this Solaris release, the zfs backup and zfs restore commands are renamed to zfs send and zfs receive to more accurately describe their function. The function of these commands is to save and restore ZFS data stream representations.
For more information about these commands, see Sending and Receiving ZFS Data.
Solaris Express Community Release, build 37: This release includes the zpool import -D command, which enables you to recover pools that were previously destroyed with the zpool destroy command.
For more information, see Recovering Destroyed ZFS Storage Pools.
Solaris Express Community Release, build 36: This release includes the integration of a ZFS diagnostic engine that is capable of diagnosing and reporting pool failures and device failures. Checksum, I/O, device, and pool errors associated with pool or device failures are also reported.
The diagnostic engine does not include predictive analysis of checksum and I/O errors, nor does it include proactive actions based on fault analysis.
In the event of the ZFS failure, you might see a message similar to the following from fmd:
SUNW-MSG-ID: ZFS-8000-D3, TYPE: Fault, VER: 1, SEVERITY: Major EVENT-TIME: Fri Aug 28 09:10:27 PDT 2009 PLATFORM: SUNW,Sun-Fire-T200, CSN: -, HOSTNAME: neo SOURCE: zfs-diagnosis, REV: 1.0 EVENT-ID: d6725ad6-4546-6c48-fa16-eace4d371981 DESC: A ZFS device failed. Refer to http://sun.com/msg/ZFS-8000-D3 for more information. AUTO-RESPONSE: No automated response will occur. IMPACT: Fault tolerance of the pool may be compromised. REC-ACTION: Run 'zpool status -x' and replace the bad device.
By reviewing the recommended action, which will be to follow the more specific directions in the zpool status command, you will be able to quickly identify and resolve the failure.
For an example of recovering from a reported ZFS problem, see Resolving a Missing Device.
Solaris Express Community Release, build 36: This release includes the zpool clear command for clearing error counts associated with a device or the pool. Previously, error counts were cleared when a device in a pool was brought online with the zpool online command. For more information, see zpool(1M) and Clearing Storage Pool Device Errors.
Solaris Express Community Release, build 34: In this release, three NFSv4 ACL formats are available: verbose, positional, and compact. The new compact and positional ACL formats are available to set and display ACLs. You can use the chmod command to set all 3 ACL formats. You can use the ls -V command to display compact and positional ACL formats and the ls -v command to display verbose ACL formats.
For more information, see Setting and Displaying ACLs on ZFS Files in Compact Format, chmod(1), and ls(1).
Solaris Express Community Release, build 34: A new file system monitoring tool, fsstat, is available to report file system operations. Activity can be reported by mount point or by file system type. The following example shows general ZFS file system activity.
$ fsstat zfs new name name attr attr lookup rddir read read write write file remov chng get set ops ops ops bytes ops bytes 7.82M 5.92M 2.76M 1.02G 3.32M 5.60G 87.0M 363M 1.86T 20.9M 251G zfs
For more information, see fsstat(1M).
Solaris Express Community Release, build 28: A web-based ZFS management tool is available to perform many administrative actions. With this tool, you can perform the following tasks:
Create a new storage pool.
Add capacity to an existing pool.
Move (export) a storage pool to another system.
Import a previously exported storage pool to make it available on another system.
View information about storage pools.
Create a file system.
Create a volume.
Take a snapshot of a file system or a volume.
Roll back a file system to a previous snapshot.
You can access the ZFS Administration console through a secure web browser at the following URL:
If you type the appropriate URL and are unable to reach the ZFS Administration console, the server might not be started. To start the server, run the following command:
# /usr/sbin/smcwebserver start
If you want the server to run automatically when the system boots, run the following command:
# /usr/sbin/smcwebserver enable
You cannot use the Solaris Management Console (smc) to manage ZFS storage pools or file systems.
The Solaris ZFS file system is a revolutionary new file system that fundamentally changes the way file systems are administered, with features and benefits not found in any other file system available today. ZFS has been designed to be robust, scalable, and simple to administer.
ZFS uses the concept of storage pools to manage physical storage. Historically, file systems were constructed on top of a single physical device. To address multiple devices and provide for data redundancy, the concept of a volume manager was introduced to provide the image of a single device so that file systems would not have to be modified to take advantage of multiple devices. This design added another layer of complexity and ultimately prevented certain file system advances, because the file system had no control over the physical placement of data on the virtualized volumes.
ZFS eliminates the volume management altogether. Instead of forcing you to create virtualized volumes, ZFS aggregates devices into a storage pool. The storage pool describes the physical characteristics of the storage (device layout, data redundancy, and so on,) and acts as an arbitrary data store from which file systems can be created. File systems are no longer constrained to individual devices, allowing them to share space with all file systems in the pool. You no longer need to predetermine the size of a file system, as file systems grow automatically within the space allocated to the storage pool. When new storage is added, all file systems within the pool can immediately use the additional space without additional work. In many ways, the storage pool works similarly to a virtual memory system. When a memory DIMM is added to a system, the operating system doesn't force you to invoke some commands to configure the memory and assign it to individual processes. All processes on the system automatically use the additional memory.
ZFS is a transactional file system, which means that the file system state is always consistent on disk. Traditional file systems overwrite data in place, which means that if the machine loses power, for example, between the time a data block is allocated and when it is linked into a directory, the file system will be left in an inconsistent state. Historically, this problem was solved through the use of the fsck command. This command was responsible for going through and verifying file system state, making an attempt to repair any inconsistencies in the process. This problem caused great pain to administrators and was never guaranteed to fix all possible problems. More recently, file systems have introduced the concept of journaling. The journaling process records action in a separate journal, which can then be replayed safely if a system crash occurs. This process introduces unnecessary overhead, because the data needs to be written twice, and often results in a new set of problems, such as when the journal can't be replayed properly.
With a transactional file system, data is managed using copy on write semantics. Data is never overwritten, and any sequence of operations is either entirely committed or entirely ignored. This mechanism means that the file system can never be corrupted through accidental loss of power or a system crash. So, no need for a fsck equivalent exists. While the most recently written pieces of data might be lost, the file system itself will always be consistent. In addition, synchronous data (written using the O_DSYNC flag) is always guaranteed to be written before returning, so it is never lost.
With ZFS, all data and metadata is checksummed using a user-selectable algorithm. Traditional file systems that do provide checksumming have performed it on a per-block basis, out of necessity due to the volume management layer and traditional file system design. The traditional design means that certain failure modes, such as writing a complete block to an incorrect location, can result in properly checksummed data that is actually incorrect. ZFS checksums are stored in a way such that these failure modes are detected and can be recovered from gracefully. All checksumming and data recovery is done at the file system layer, and is transparent to applications.
In addition, ZFS provides for self-healing data. ZFS supports storage pools with varying levels of data redundancy. When a bad data block is detected, ZFS fetches the correct data from another redundant copy, and repairs the bad data, replacing it with the good copy.
ZFS has been designed from the ground up to be the most scalable file system, ever. The file system itself is 128-bit, allowing for 256 quadrillion zettabytes of storage. All metadata is allocated dynamically, so no need exists to pre-allocate inodes or otherwise limit the scalability of the file system when it is first created. All the algorithms have been written with scalability in mind. Directories can have up to 248 (256 trillion) entries, and no limit exists on the number of file systems or number of files that can be contained within a file system.
A snapshot is a read-only copy of a file system or volume. Snapshots can be created quickly and easily. Initially, snapshots consume no additional space within the pool.
As data within the active dataset changes, the snapshot consumes space by continuing to reference the old data. As a result, the snapshot prevents the data from being freed back to the pool.
Most importantly, ZFS provides a greatly simplified administration model. Through the use of hierarchical file system layout, property inheritance, and automanagement of mount points and NFS share semantics, ZFS makes it easy to create and manage file systems without needing multiple commands or editing configuration files. You can easily set quotas or reservations, turn compression on or off, or manage mount points for numerous file systems with a single command. Devices can be examined or repaired without having to understand a separate set of volume manager commands. You can take an unlimited number of instantaneous snapshots of file systems. You can backup and restore individual file systems.
ZFS manages file systems through a hierarchy that allows for this simplified management of properties such as quotas, reservations, compression, and mount points. In this model, file systems become the central point of control. File systems themselves are very cheap (equivalent to a new directory), so you are encouraged to create a file system for each user, project, workspace, and so on. This design allows you to define fine-grained management points.
This section describes the basic terminology used throughout this book:
A boot environment that is created by the lucreate command and possibly updated by the luupgrade command, but it is not currently the active or primary boot environment. The alternate boot environment (ABE) can be changed to the primary boot environment (PBE) by running the luactivate command.
A file system whose initial contents are identical to the contents of a snapshot.
For information about clones, see Overview of ZFS Clones.
A generic name for the following ZFS entities: clones, file systems, snapshots, or volumes.
Each dataset is identified by a unique name in the ZFS namespace. Datasets are identified using the following format:
Identifies the name of the storage pool that contains the dataset
Is a slash-delimited path name for the dataset object
Is an optional component that identifies a snapshot of a dataset
For more information about datasets, see Chapter 6, Managing ZFS File Systems.
A ZFS dataset of type filesystem that is mounted within the standard system namespace and behaves like other file systems.
For more information about file systems, see Chapter 6, Managing ZFS File Systems.
A logical group of devices describing the layout and physical characteristics of the available storage. Space for datasets is allocated from a pool.
For more information about storage pools, see Chapter 4, Managing ZFS Storage Pools.
A boot environment that is used by the lucreate command to build the alternate boot environment. By default, the primary boot environment (PBE) is the current boot environment. This default can be overridden by using the lucreate -s option.
A virtual device that stores data and parity on multiple disks. For more information about RAID-Z, see RAID-Z Storage Pool Configuration.
The process of transferring data from one device to another device is known as resilvering. For example, if a mirror component is replaced or taken offline, the data from the up-to-date mirror component is copied to the newly restored mirror component. This process is referred to as mirror resynchronization in traditional volume management products.
For more information about ZFS resilvering, see Viewing Resilvering Status.
A read-only image of a file system or volume at a given point in time.
For more information about snapshots, see Overview of ZFS Snapshots.
A logical device in a pool, which can be a physical device, a file, or a collection of devices.
For more information about virtual devices, see Displaying Storage Pool Virtual Device Information.
A dataset used to emulate a physical device. For example, you can create a ZFS volume as a swap device.
For more information about ZFS volumes, see ZFS Volumes.
Empty components are not allowed.
Each component can only contain alphanumeric characters in addition to the following four special characters:
Pool names must begin with a letter, except for the following restrictions:
The beginning sequence c[0-9] is not allowed
The name log is reserved
A name that begins with mirror, raidz, raidz1, raidz2, raidz3, or spare is not allowed because these name are reserved.
In addition, pool names must not contain a percent sign (%)
Dataset names must begin with an alphanumeric character. Dataset names must not contain a percent sign (%).