zfs discuss - Nov 2008 - Downgrading a zpool

I probably need to downgrade a machine from 10u5 to 10u3. The zpool on  
u5 is a v4 pool, and AIUI 10u3 only supports up to v3 pools.

Will this pool automatically import when I downgrade the OS?

Assuming I''m not that lucky, can I use 10u5''s zfs send to take
a
backup of the filesystems, and zfs receive on 10u3 to restore them?

Cheers,

Chris

Chris Ridd wrote:
> I probably need to downgrade a machine from 10u5 to 10u3. The zpool on  
> u5 is a v4 pool, and AIUI 10u3 only supports up to v3 pools.
>
> Will this pool automatically import when I downgrade the OS?
>
>   
No you are out of luck.
> Assuming I''m not that lucky, can I use 10u5''s zfs send to
take a
> backup of the filesystems, and zfs receive on 10u3 to restore them?
>
>   
Same again. You can''t receive a stream sent from a newer pool version.

-- 
Ian.

On 6 Nov 2008, at 09:53, Ian Collins wrote:
> Chris Ridd wrote:
>> I probably need to downgrade a machine from 10u5 to 10u3. The zpool  
>> on
>> u5 is a v4 pool, and AIUI 10u3 only supports up to v3 pools.
>>
>> Will this pool automatically import when I downgrade the OS?
>>
>>
> No you are out of luck.
I thought that might be the case :-)
>> Assuming I''m not that lucky, can I use 10u5''s zfs
send to take a
>> backup of the filesystems, and zfs receive on 10u3 to restore them?
>>
>>
> Same again. You can''t receive a stream sent from a newer pool
version.
That''s a pity. I''m slightly surprised that the pool version
affects
the filesystem/snapshot stream format.

Cheers,

Chris

On 6 Nov 2008, at 10:19, Christian Vallo wrote:
> Hi Chris,
>
> i think there is no way to downgrade. I think you must copy/sync the  
> data from one pool (v4) to another pool (v3).
Darn. I''ve managed to push back on doing the downgrade for now
anyway...

Cheers,

Chris

On Thu, 6 Nov 2008, Chris Ridd wrote:
> I probably need to downgrade a machine from 10u5 to 10u3. The zpool on 
> u5 is a v4 pool, and AIUI 10u3 only supports up to v3 pools.
The only difference between a v4 pool and a v3 pool is that v4 added 
history (''zpool history <pool>'').  I would expect a v3
pool to be able to
receive a v4 send stream, as the zpool history is not part of ''zfs
send''.

Trying this out on my nevada box:

--------------------------------------------------------------------------------
-bash-3.2# zpool create -o version=3 v3pool c0t1d0s0
-bash-3.2# zpool create -o version=4 v4pool c0t2d0s0
-bash-3.2# zpool status
   pool: v3pool
  state: ONLINE
status: The pool is formatted using an older on-disk format.  The pool can
         still be used, but some features are unavailable.
action: Upgrade the pool using ''zpool upgrade''.  Once this is
done, the
         pool will no longer be accessible on older software versions.
  scrub: none requested
config:

         NAME        STATE     READ WRITE CKSUM
         v3pool      ONLINE       0     0     0
           c0t1d0s0  ONLINE       0     0     0

errors: No known data errors

   pool: v4pool
  state: ONLINE
status: The pool is formatted using an older on-disk format.  The pool can
         still be used, but some features are unavailable.
action: Upgrade the pool using ''zpool upgrade''.  Once this is
done, the
         pool will no longer be accessible on older software versions.
  scrub: none requested
config:

         NAME        STATE     READ WRITE CKSUM
         v4pool      ONLINE       0     0     0
           c0t2d0s0  ONLINE       0     0     0

errors: No known data errors
-bash-3.2# zfs create v4pool/foobar
-bash-3.2# mkfile 1m /v4pool/foobar/1meg
-bash-3.2# ls -l /v4pool/foobar/1meg
-rw------T   1 root     root     1048576 Nov  6 05:53 /v4pool/foobar/1meg
-bash-3.2# zfs snapshot v4pool/foobar at snap
-bash-3.2# zfs send v4pool/foobar at snap | zfs recv v3pool/foobar at snap
-bash-3.2# ls -l /v3pool/foobar
total 2053
-rw------T   1 root     root     1048576 Nov  6 05:53 1meg
-bash-3.2# zfs list
NAME                 USED  AVAIL  REFER  MOUNTPOINT
v3pool              1.09M   134G    20K  /v3pool
v3pool/foobar       1.02M   134G  1.02M  /v3pool/foobar
v3pool/foobar at snap      0      -  1.02M  -
v4pool              1.09M   134G    20K  /v4pool
v4pool/foobar       1.02M   134G  1.02M  /v4pool/foobar
v4pool/foobar at snap      0      -  1.02M  -
-bash-3.2# 
--------------------------------------------------------------------------------

Works fine.


Regards,
markm