FreeBSD ZFS – Connecting an existing zpool to a new OS

Imagine that you have your server with an external RAID array running a ZFS file system, or even a separate internal array on the box and the OS array is trashed. Now you have your nice redundant ZFS partition, but no operating system to address it! To test this I have my usual HP MicroServer with 3 x 2TB WD Green drives in it and I have removed the OS disk which runs PCBSD. The new OS disk has FreeBSD 9.0 RC1 on it – I was using it to test jails, but would like to now hook up the 3 ZFS drives as they were attached to the old OS. I had a quick scan through the help files (man zpool) and the 'import' command seemed the most appropriate:

jtest# zpool list
no pools available
jtest# zpool import
  pool: DATA
    id: 8060566178365973247
 state: ONLINE
status: The pool is formatted using an older on-disk version.
action: The pool can be imported using its name or numeric identifier, though
	some features will not be available without an explicit 'zpool upgrade'.

	  raidz1-0  ONLINE
	    ada1    ONLINE
	    ada2    ONLINE
	    ada3    ONLINE

Ok so its found the old ‘DATA’ zpool I had set up, seems that I can just import it…

jtest# zpool import DATA
jtest# zpool list
DATA  5.44T  1.16G  5.44T     0%  1.00x  ONLINE  -

Right, now i’d like to upgrade the zpool to the latest greatest:

jtest# zpool upgrade
This system is currently running ZFS pool version 28.

The following pools are out of date, and can be upgraded.  After being
upgraded, these pools will no longer be accessible by older software versions.

---  ------------
15   DATA

Use 'zpool upgrade -v' for a list of available versions and their associated

That command just displays options, but I’m interested to find out the extra features, so i’ll do as the output advises:

jtest# zpool upgrade -v
This system is currently running ZFS pool version 28.

The following versions are supported:

---  --------------------------------------------------------
 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
 27  Improved snapshot creation performance
 28  Multiple vdev replacements

For more information on a particular version, including supported releases,
see the ZFS Administration Guide.

The deduplication feature looks good so i’ll just go for it!

jtest# zpool upgrade DATA
This system is currently running ZFS pool version 28.

Successfully upgraded 'DATA' from version 15 to version 28

Fantastic! As you can see all the data is there and readable from before.

cd /DATA/dans_stuff/
jtest# ls -lah
total 811440
drwxr-xr-x  3 root  wheel     4B Oct 17 20:50 .
drwxr-xr-x  3 root  wheel     3B Oct 17 20:50 ..
dr-xr-xr-x  4 root  wheel     4B Oct 17 20:47 .zfs
-rw-r--r--  1 root  wheel   1.0G Oct 17 20:50 FreeBSD-8.2-RELEASE-amd64-memstick.img
-rw-r-----  1 root  wheel   263M Oct 17 20:43 maillog

Last thing is to ensure that deduplication is activated with the following command:

zfs set dedup=on DATA

Verify with:

jtest# zfs get dedup DATA
DATA  dedup     on             local
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