Because I need to help some friend with backup up data from his broken PC I need to temporary remove my 2TB disks from my zfs pool so I have enough diskspace.
This is my current pool with the status:
file# zpool status
pool: tank
state: ONLINE
status: One or more devices is currently being resilvered. The pool will
continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
scrub: resilver in progress for 0h18m, 28.93% done, 0h45m to go
config:
NAME STATE READ WRITE CKSUM
tank ONLINE 0 0 0
mirror ONLINE 0 0 0
ad8 ONLINE 0 0 0
ad6 ONLINE 0 0 0 83.7G resilvered
mirror ONLINE 0 0 0
ad10 ONLINE 0 0 0
ad14 ONLINE 0 0 0
errors: No known data errors
file# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
tank 2.27T 550G 1.73T 23% ONLINE -
file# zpool iostat -v
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
tank 550G 1.73T 4 0 348K 48.0K
mirror 294G 1.53T 875 47 78.1M 86.8K
ad8 - - 3 0 391K 51.8K
ad6 - - 0 773 235 78.1M
mirror 256G 208G 4 0 293K 47.9K
ad10 - - 2 0 294K 47.9K
ad14 - - 2 0 294K 47.9K
---------- ----- ----- ----- ----- ----- -----
file#
As you see I have 2TB disks and 2 500GB disks both in a mirror in my pool. The plan is to remove the 2TB disks from the pool, and store the data temporary on the 2 500GB disks. This means I will temporary loose some duplication, but I cant help that really 
.Right now, the plan is as follows:
Remove the first 2TB disks from the mirror, create a new pool with just this disk, and move all data from the other pool to this new pool. After this, I can destroy the pool temporary and create a new pool to store the data temporary. This seems pretty easy, doesnt it? 
It actually took me some time to find out the best way to do it, as I dont want to loose any data.
To create the new pool the following commands are needed:
file# zpool detach tank /dev/ad8 file# zpool create tank2 /dev/ad8 file# zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 2.27T 550G 1.73T 23% ONLINE - tank2 1.81T 75K 1.81T 0% ONLINE -
Now the new pool exists, the temporary data need to be moved from the old pool to the temporary new pools:
file# zfs list NAME USED AVAIL REFER MOUNTPOINT tank 550G 1.69T 66K /tank tank/annemarie 30.6G 1.69T 30.6G /tank/annemarie tank/annemarie/muziek 1.89M 2.00G 1.89M /tank/annemarie/muziek tank/dell 128G 372G 126G /tank/dell tank/downloads 220G 1.69T 220G /tank/downloads tank/open 6.04G 494G 6.04G /tank/open tank/prive 21K 1.69T 21K /tank/prive tank/toshiba 79.1G 121G 78.9G /tank/toshiba tank/zolder 86.1G 1.69T 86.1G /tank/zolder tank2 70.5K 1.78T 21K /tank2 file# zfs create tank2/annemarie file# zfs create tank2/annemarie/muziek file# zfs create tank2/dell file# zfs create tank2/downloads file# zfs create tank2/toshiba file# zfs create tank2/zolder
Besides creating the (actually unneeded, but ok) several existing mounts, I enabled compression on them as well. After that, I just did:
file# time cp -r /tank /tank2
But after a few minutes I already discovered a few issues, as it was missing files and the speed was not really good. So I decided to go with rsync after a few minutes, and it looks like thats going lots faster.
Once all data was copied I can remove the other 2TB disk:
file# zpool detach tank /dev/ad6 cannot detach /dev/ad6: only applicable to mirror and replacing vdevs
This is pretty logical, as this action will make all data lost. I want that in this case, but normally you don’t .
So instead, I just destroy the pool:
file# zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 2.27T 548G 1.73T 23% ONLINE - tank2 1.81T 565G 1.26T 30% ONLINE - file# zpool destroy tank file# zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank2 1.81T 565G 1.26T 30% ONLINE -
And now create a new pool with the 2 500GB disks:
file# zpool create tank /dev/ad10 /dev/ad14 file# zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 928G 78K 928G 0% ONLINE - tank2 1.81T 565G 1.26T 30% ONLINE - file# zpool status pool: tank state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank ONLINE 0 0 0 ad10 ONLINE 0 0 0 ad14 ONLINE 0 0 0 errors: No known data errors pool: tank2 state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank2 ONLINE 0 0 0 ad8 ONLINE 0 0 0 errors: No known data errors file# zpool add tank2 /dev/ad6 file# zpool status pool: tank state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank ONLINE 0 0 0 ad10 ONLINE 0 0 0 ad14 ONLINE 0 0 0 errors: No known data errors pool: tank2 state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank2 ONLINE 0 0 0 ad8 ONLINE 0 0 0 ad6 ONLINE 0 0 0 errors: No known data errors file# zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT tank 928G 78K 928G 0% ONLINE - tank2 3.62T 565G 3.07T 15% ONLINE - file#
Besides creating the new pool I also added the other 2TB disk to the temporary pool that I needed in first case .
Now the only thing I need to do is move all data from /tank2 to /tank and we are done .
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