Hi,

I recently did a system upgrade that I'm rolling back. On the newer system I expanded a single drive pool into a mirrored pool. Now I have to revert that mirror into a single drive again. The challenge is that I only have one m.2 slot on this older system so I have to revert it to a single drive without the full mirror being present. Right now it is successfully mounting but is marked as degraded. I'm sure there is some straightforward way to do it but I've looked and looked and haven't found it. If someone could please point me in the right direction that would be very helpful.

What kind of pool filesystem? Also clicking on the pool name and posting a screenshot of the pool status/information would be helpful.

Thank you for the reply! Screenshot attached, it's the Nvme pool that I need to remove a device from. Right now the red triangle next to the existing drive says "Device has an error status: CANT_OPEN" which I've never seen before. It's also inaccurate since the drive is mounted and operating.

Anyone wondering how I have dark mode, I use the Dark Reader extension which works very well and is available on Chrome and Firefox.

Edited September 14Sep 14 by gusgus

Please post the diagnostics.

Diagnostics here

metaverse-diagnostics-20260914-0848.zip

zfs is detecting data corruption on the remaining device, so I recommend running memtest first, then using zpool status -v to see the corrupt file(s) and delete/restore from a backup.

Thank you @JorgeB! I guess unRAID hasn't integrated zfs data integrity issues properly into the UI yet.

@JorgeB after resolving this will I be able to remove the second mirror drive from the pool?

That needs to be done in a second step, post new diags once that's resolved.

 Ok finally the corrupted file has been deleted, but the CANT_OPEN error is still on the existing nvme drive. A look at zpool status -v says: 

errors: Permanent errors have been detected in the following files:

        nvme:<0x10f>

metaverse-diagnostics-20260923-1850.zip

Edited September 24Sep 24 by gusgus

The "can't open" error is a bug, and just a display issue, the corruption is a problem, and the error typically means metadata corruption. Try scrubbing the pool, if the error remains, my recommendation would be to back up and recreate the pool.

A scrub cleared it up, zpool status -v now says

errors: No known data errors

So it looks like the next step is to remove the extraneous mirror device in the Nvme pool. How would I go about doing that?

Thank you JorgeB for all your help! Definitely will be sending beer money when this is over!

metaverse-diagnostics-20260924-1751.zip

With the array running type

zpool detach nvme 13874904942354296596

Then stop the array and reimport the pool with the remaining device:

on main click on the first device for that pool and then "remove pool"

back on main, create a new pool with the same name and 1 slot

assign the pool device, leave the filesystem set to auto

start the array to import the pool

Worked perfectly! Thank you JorgeB for all of the help!