Adding slight smaller replacement disk to pool

OpenZFS
1

Hello ZFS Gurus,

I have a pool that is mostly made up of “Samsung SSD 860 PRO 4TB” drives and would like to begin replacing these with “Kingston DC600M 3.84 TB” drives.

My questions:

  1. Will adding the slightly smaller disk automatically cause the pool to default to the smaller size disk?
  2. or should I instead add a larger disk to the pool

ZFS:
zfs-0.8.3-1ubuntu12.17
zfs-kmod-2.1.5-1ubuntu6~22.04.4

Ubuntu Server: 20.04

Thanks!

2

You aren’t going to be able to replace them one by one. ZFS will throw an error at you (safely) if you try.

You definitely picked a winner for your new drive model, but unfortunately you’ll need to build a new pool and replicate data in from your existing pool.

The only other option would be to return the 3.84s, and get 7.68s instead. You’d obviously be spending twice as much, but end up with double the capacity, and you’d still be able to replace drives one by one.

3

Thanks Jim for pointing out the details. Very helpful as always. I will probably go the 7.68 drive route instead.

I appreciate it!!

1 Like
4

So, no, you cannot simply do a ZFS replace of the old drives with the new ones. Depending on the current layout of your pool and the availability of empty SATA ports on your system, a migration path may be possible without migrating to a new pool.

If you want to post the output of the following commands, we might be able to give more detailed advice:

  • lsblk -bo NAME,LABEL,MAJ:MIN,TRAN,ROTA,ZONED,VENDOR,MODEL,SERIAL,PARTUUID,START,SIZE,PARTTYPENAME
  • sudo zpool status -v
  • ls -l /sys/bus/scsi/devices

Your ubuntu and zfs are quite old, so you may need to adjust the lsblk command to remove any individual fields that it objects to.