ZFS Property Enhancements

Solaris 10 10/09 and Oracle Solaris 10 9/10: The following ZFS file system enhancements are included in these releases.

• ZFS Snapshot Stream Property Enhancements – You can set a received property that is different from its local property setting. For example, you might receive a stream with the compression property disabled, but you want compression enabled in the receiving file system. This means that the received stream has a received compression value of off and a local compression value of on. Since the local value overrides the received value, you don't have to worry about the setting on the sending side replacing the received side value. The zfs get command shows the effective value of the compression property under the VALUE column.

  New ZFS command options and properties to support send and local property values are as follows:

  • Use the zfs inherit -S to revert a local property value to the received value, if any. If a property does not have a received value, the behavior of the zfs inherit -S command is the same as the zfs inherit command without the -S option. If the property does have a received value, the zfs inherit command masks the received value with the inherited value until issuing a zfs inherit -S command reverts it to the received value.

  • You can use the zfs get -o to include the new non-default RECEIVED column. Or, use the zfs get -o all command to include all columns, including RECEIVED.

  • You can use the zfs send -p option to include properties in the send stream without the -R option.

  In addition, you can use the zfs send -e option to use the last element of the sent snapshot name to determine the new snapshot name. The following example sends the poola/bee/cee@1 snapshot to the poold/eee file system and only uses the last element (cee@1) of the snapshot name to create the received file system and snapshot.

  # zfs list -rt all poola NAME USED AVAIL REFER MOUNTPOINT poola 134K 134G 23K /poola poola/bee 44K 134G 23K /poola/bee poola/bee/cee 21K 134G 21K /poola/bee/cee poola/bee/cee@1 0 - 21K - # zfs send -R poola/bee/cee@1 | zfs receive -e poold/eee # zfs list -rt all poold NAME USED AVAIL REFER MOUNTPOINT poold 134K 134G 23K /poold poold/eee 44K 134G 23K /poold/eee poold/eee/cee 21K 134G 21K /poold/eee/cee poold/eee/cee@1 0 - 21K -

• Setting ZFS file system properties at pool creation time – You can set ZFS file system properties when a storage 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 enable you to control what is cached in the primary cache (ARC) and 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 a file system is created. For example:

  # zfs set primarycache=metadata tank/datab # zfs create -o primarycache=metadata tank/newdatab

  When these properties are set on existing file systems, only new I/O is cache based on the values of these properties.

  Some database environments might benefit from not caching user data. You must determine if setting cache properties is appropriate for your environment.

• Viewing disk space accounting properties – New read-only file system properties help you identify disk space usage for clones, file systems, and volumes, and snapshots. The properties are as follows:

  • usedbychildren – Identifies the amount of disk 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 disk 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 disk 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 disk space that is consumed by snapshots of this dataset, which would be freed if all of this dataset's snapshots were destroyed. Note that this is not the sum of the snapshots' used properties, because disk 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 disk 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 preceding 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 on, which means snapshot information is displayed by default.

  If your system has many ZFS snapshots and you wish to disable the display of snapshot information in the zfs list command, disable the listsnapshots property as follows:

  # zpool get listsnapshots pool NAME PROPERTY VALUE SOURCE pool listsnapshots on default # zpool set listsnaps=off pool

  If you disable the listsnapshots property, you can use the zfs list -t snapshots command to list 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 -