Hi,

I want to attach a second HD to an existin pool to create a mirror:

The current pool is:

root@unraid:~# zpool status
  pool: disk1
 state: ONLINE
  scan: scrub repaired 0B in 00:10:14 with 0 errors on Fri Oct 17 16:21:29 2025
config:
	NAME        STATE     READ WRITE CKSUM
	disk1       ONLINE       0     0     0
	  md1p1     ONLINE       0     0     0

With zpool attach I could convert this into a mirror:

https://openzfs.github.io/openzfs-docs/man/master/8/zpool-attach.8.html

But how do I do that with unraid? Does the GUI support this operation or do I need to do it on the commandline. Also, the current pool is encrypted resp. teh device is a LUKS device created by unraid during initial setup. What is the best way to attach a second drive?

You cannot add a mirror to an array device; you can reimport that device as a single device pool, and then use the GUI to add a mirror.

The pool is a single device pool. It contains only /dev/md1p1. See zpool status in my previous post. What do you mean with "reimport that device as a single device pool"?

18 hours ago, mabod said:

The pool is a single device pool.

md1p1 is an array device not a pool. You can click the "add pool" button with the array stooped, do a new config and reassign that device to a pool instead of the array (disk1, disk2, etc)

Note that although Unraid allows for ZFS format on array disks, these can only be single device pools as each array disk must contain a free-standing file system.