Hi folks, so before touching anything further, I wanted to seek some advice.

Recently I had some issues with my previous motherboard/psu that made unraid go a little bonkers with the read errors.

During my troubleshooting, I attempted to remove a drive that became unmountable, start the array in maintenance mode, turn it off, start it again and rebuild on that same drive but since I started getting more and more errors on more drives, I decided to turn off everything.

As it stands now, I replaced all the parts/cables that could be culprits and I stopped getting read errors on all my drives, I want to attempt a rebuild on that drive but it shows as unmountable, should I assign it at the same spot and start a rebuild or do a format and then rebuild??

I would like to know the steps about it, I checked the docs but it seems that my scenario is a bit unusual so I would like to make sure before proceeding.

I started the data rebuild initially but from what I've seen in the docs/forums, a data rebuild on an unmountable drive results in an unmountable drive regardless?

What should I do then format the drive and the assign it to the same spot in the array?

Any help would be appreciated. If I have to lose data on said drive I can take that hit but would rather avoid it if possible.

Thanks again for any advice and merry Christmas.

As it stands here is the status of my array (stopped, and the unassigned device is the one I wish to put back):

Before doing anything else, start the array as is, with disk2 unassigned, and post the diagnostics.

4 minutes ago, JorgeB said:

Before doing anything else, start the array as is, with disk2 unassigned, and post the diagnostics.

Thanks for the tip, I don't know if you remember me from a few weeks ago, I was the person with this issue:

I took the radical approach of replacing, the mobo, the psu and all related power/sata cables and rebuilding all from scratch, the issues I had seem to be gone now and I don't get anymore read errors so my guess is that it was either the motherboard controller failing, the psu or the cables which I will trouble shoot later.

Here are my diagnostics after leaving the drive unassigned and starting the array.

taichi-diagnostics-20251225-1428.zip

(I stopped the array after generating the diagnostics)

Edited December 25, 2025Dec 25 by MonadProxy

36 minutes ago, MonadProxy said:

I started the data rebuild initially but from what I've seen in the docs/forums, a data rebuild on an unmountable drive results in an unmountable drive regardless?

Yes. Check filesystem is the correct approach before trying anything else with an unmountable drive.

38 minutes ago, MonadProxy said:

What should I do then format the drive and the assign it to the same spot in the array?

If you format a disk in the array then rebuild, the result will be a formatted disk. Format is never part of rebuild.

If you format or do anything else to a disk outside the array, it is just wasted effort, since rebuild will completely overwrite the disk anyway.

6 minutes ago, MonadProxy said:

Here are my diagnostics after leaving the drive unassigned and starting the array.

Emulated disk2 is unmountable. Check filesystem on emulated disk2.

4 minutes ago, trurl said:

Yes. Check filesystem is the correct approach before trying anything else with an unmountable drive.

If you format a disk in the array then rebuild, the result will be a formatted disk. Format is never part of rebuild.

If you format or do anything else to a disk outside the array, it is just wasted effort, since rebuild will completely overwrite the disk anyway.

Emulated disk2 is unmountable. Check filesystem on emulated disk2.

So do you mean by that if I leave disk2 unassigned, start the array in non-maintenance mode, run a read-check on the array and then what if it comes up ok? Sorry I am just trying to make sure before pushing buttons.

Leave the disk2 slot not assigned. Disk2 is emulated by the parity calculation by reading parity plus all other disks in the array. Unfortunately, the result of that emulation is an unmountable disk. If you rebuild disk2 when the emulated disk is unmountable, the result will be an unmountable disk.

What you suggest is not at all what I mean. Did you read the check filesystem link?

44 minutes ago, trurl said:

Leave the disk2 slot not assigned. Disk2 is emulate by the parity calculation by reading parity plus all other disks in the array. Unfortunately, the result of that emulation is an unmountable disk. If you rebuild disk2 when the emulated disk is unmountable, the result will be an unmountable disk.

What you suggest is not at all what I mean. Did you read the check filesystem link?

I am attempting a read check (in maintenance mode for xfs as advised) without disk 2 and if the result is okay should i re-add the disk and attempt a re-build will the unmountable message go away if the read check goes okay?

Edited December 25, 2025Dec 25 by MonadProxy

6 minutes ago, MonadProxy said:

I am attempting a read check (in maintenance mode for xfs as advised) without disk 2 and if the result is okay should i re-add the disk and attempt a re-build will the unmountable message go away if the read check goes okay?

No.

The only way to clear an unmountable state is to fix the file system level corruption (assuming it can be fixed).

41 minutes ago, itimpi said:

No.

The only way to clear an unmountable state is to fix the file system level corruption (assuming it can be fixed).

Ok, I went to re-read the docs and yeah I misunderstood what you had said so after I ran the check button on that specific emulated drive and it fixed itself, the second check returned no errors and I could proceed with the parity rebuild. No more unmountable or wrong filesystem messages. Thanks.

On 12/25/2025 at 5:22 PM, MonadProxy said:

a read check (in maintenance mode for xfs

Just for completeness, this is not a Read Check, it is a Filesystem Check.

The webUI will let you do a Read Check instead of a Parity Check in Array Operation when there is already a disabled disk (or 2 for dual parity) since it can't do a parity check. It will just check that all remaining disks can be read.