As features are added to ZFS - the ZFS (filesystem) code may change and/or the underlying ZFS POOL code may change. When features are added, older versions of ZFS/ZPOOL will not be able to take advantage of these new features without the ZFS filesystem and/or pool being updated first.
Since ZFS filesystems exist inside of ZFS pools, the ZFS pool may need to be upgraded before a ZFS filesystem upgrade may take place. For instance, in ZFS pool version 24, support for system attributes was added to ZFS. To allow ZFS filesystems to take advantage of these new attributes, ZFS filesystem version 4 (or higher) is required. The proper order to upgrade would be to bring the ZFS pool up to at least version 24, and then upgrade the ZFS filesystem(s) as needed.
Systems running a newer version of ZFS (pool or filesystem) may "understand" an earlier version. However, older versions of ZFS will not be able to access ZFS streams from newer versions of ZFS.
For NexentaStor users, here are the current versions of the ZFS filesystem (see "zfs upgrade -v"):
VER DESCRIPTION
--- --------------------------------------------------------
1 Initial ZFS filesystem version
2 Enhanced directory entries
3 Case insensitive and File system unique identifier (FUID)
4 userquota, groupquota properties
5 System attributes
For NexentaStor users, here are the current versions of the ZFS pool (see "zpool upgrade -v"):
VER DESCRIPTION
--- --------------------------------------------------------
1 Initial ZFS version
2 Ditto blocks (replicated metadata)
3 Hot spares and double parity RAID-Z
4 zpool history
5 Compression using the gzip algorithm
6 bootfs pool property
7 Separate intent log devices
8 Delegated administration
9 refquota and refreservation properties
10 Cache devices
11 Improved scrub performance
12 Snapshot properties
13 snapused property
14 passthrough-x aclinherit
15 user/group space accounting
16 stmf property support
17 Triple-parity RAID-Z
18 Snapshot user holds
19 Log device removal
20 Compression using zle (zero-length encoding)
21 Deduplication
22 Received properties
23 Slim ZIL
24 System attributes
25 Improved scrub stats
26 Improved snapshot deletion performance
As versions change, upgrading the ZFS pool and filesystem is possible using the respective upgrade command. To upgrade all imported ZFS pools,
issue the following command as root:
zpool upgrade -a
Likewise, to upgrade the ZFS filesystem(s) inside the pool and all child filesystems,
issue the following command as root:
zfs upgrade -r -a
The new ZFS features available to these pool and filesystem version(s) will now be available to the upgraded pools/filesystems.
