ZFS Zpool upgrade question

[Paul Kraus]

On 9/9/14 11:21, bsd at todoo.biz wrote:
> Hi folks,
>
> We have moved our server from 9.2 to 9.3 and there seem to be a new version of ZFS available with a new feature set.
>
> We are backing up our data on FreeNAS which has the same ZFS version for the moment.
>> ZFS filesystem version: 5
>> ZFS storage pool version: features support (5000)
> • Can we leave with a non updated version of a ZPool on a server? What are the risks ?
You can leave the zpool (and zfs) at a lower version.
I am not aware of any risks per-se, but you will not get the additional 
features of the newer version. In some cases the features fix bugs 
(usually for corner cases, but bugs just the same). So if you run into a 
situation where you need a fix a feature provides you may get into 
trouble. A past example I have ran into was poor zfs destroy performance 
with _lots_ of snapshots. IIRC the specific problem I was having on 
zpool 15 was fixed by the time zpool 28 was out.

> • Can my server zfs send | receive It’s data on different version of ZFS on send <> receive side ?
According to the man page, the format of the zfs stream is committed and 
you are supposed to be able to zfs send / zfs recv between different 
versions of ZFS. Just be aware that if you are using a specific feature 
on one end you may not have that functionality on the other.

I kept my zpools at version 28 for over a year so I would have a the 
flexibility of moving the zpool to a different OS system (zpool 28 was 
the last version completely supported by Solaris / Illumos / FreeBSD, 
after that there have been added features that may or may not be on one 
OS or the other).