ZFS and special device how to use unused free space ?

[guletz]

Is this even possible to do ?

Hi,

I think you can do if you want. You need an extra SSD(= extra) that you will use in the migration process:

FOR each NVME1/2 DO:

- replace one of your NVME(=nvmeX) with "extra", and wait for resilver process to finish
- repartition your NVME as you like(one part for special dev, and the rest for whatever else)
- replace the "extra" with the "special dev part" of the nvmeX
- wait for resilver

END

In the end, you will have 2 partitions on each NVME, one who is "zfs special dev" and a second partition who can be used as you like!

Good luck!

 

[chengkinhung]

Hi, every one,

I have setup special+log+cache into rpool and was running well, now this ProxMox can not boot and hang in grub recuse mode, so I want to remove the special ,log and cache device. I know i can remove log and cache device any time, but i do not know if i can remove special device, could anybody tell me ? Thanks.

 

[guletz]

but i do not know if i can remove special device

Hi,

The special device is part of the pool, so you can not remove it without loose your pool/data!

Good luck / Bafta!

 

[chengkinhung]

Hi, guletz, thanks for your reply. Is there a way to move the data from special device to other pool ?

 

[guletz]

Is there a way to move the data from special device to other pool ?

Hi again,

I do not know if it is possible. But, you can send your pool on another pool(local or remote) via pve-zsync or any script who can do zfs send/recive.
Then you can destroy your pool, create a new one(without special device) and then add the data back from the "another pool"(send/recive...)

Good luck / Bafta!

 

[H4R0]

As long as it's not a raidz pool you can remove the special device.

 

[chengkinhung]

Hi,

@gu1u , thanks for your advice. Yes I can backup all VMs, and then destroy zpool, and then recreate it , and then restore VMs from backup, but that is not what I want. Thanks anyway.
@H4R0 , thanks for your reply. my special device is only one device on nvme disk, but the zpool itself is mirror with two disks, will the removing action relocate the current data saved in special device automatically ? as there is 3G data size used in my special device, I do not know how to safely remove this special device without lost current data.

P.S. my special_small_blocks size is zero, so there is not small files saved into special device.

 

[chengkinhung]

Hi, I found this:
https://forums.servethehome.com/ind...ation-classes-special-vdev.28862/#post-267459

c.
A vdev remove (you can remove slog, l2arc, mirrors and special vdevs) copies its content back to the pool (other vdevs). To be save, just force a special vdev to same ashift than other vdevs.

I will try later and update my result here. Thanks, everyone.

 

[H4R0]

There is no loss of data it just may take some time to complete.

 

[chengkinhung]

Hi, @H4R0 , thanks very much for your help.

Yes, you are right. I just run the "zpool remove rpool nvme0n1p1" and removed the special device(nvme0n1p1) from my zpool(rpool) successfull without lost any data, it take almost one minute to allocate the data from special device to other vdev devices. And one thing should be noted: I have to stop all VMs to prevent data writing.