Hi
For some time now, I’ve had a problem. One of the drives, specifically the fourth drive, sometimes disconnects (get Unassigned) while the Unraid server is running. And since I’m an amateur, I didn’t shut down the server twice as you suppose to (to get missing disk state),” and then I either re-added it or replaced it with another drive. I only powered down on once, and it seems that instead of a data rebuild, it was doing a disk clear. So my question is: are those data recoverable, since a parity check has already been performed? And today I tried to recover the data from the last parity check, but unfortunately, that drive is now empty.

Your description seems incomplete or incorrect.

You mentioned replacing disks. Do you still have the original disk? It might contain some data.

Attach Diagnostics ZIP to your NEXT post in this thread.

i have original disk but its empty

walserv-diagnostics-20250824-1203.zip

Your cache drive is logging media errors. You should run an extended SMART test on it.

I suspect there are several things missing from your description.

Possibly the word "clear" should not have been used. Unraid will only clear a disk if it is added to a new data slot in an array that has valid parity. This is so parity will remain valid. Unraid does not clear a replaced disk. And "clear" will take a long time since zeros has to be written to the entire disk, and the webUI will also say that a disk is being cleared. So clear didn't happen unless you added a disk to a new slot, and there shouldn't be any doubt whether or not it was happening.

Did you perhaps format the disk? Many people don't really understand what format means. Format means write an empty filesystem to this disk. Unraid treats format in the parity array exactly as it does any other write operation, by updating parity so it agrees with the write operation. Unlike "clear", Format doesn't take very long. After formatting a disk in the array, the only thing that can be rebuilt from parity on that data slot is an empty filesystem.

Looks like emulated disk4 was mountable when rebuild began, but probably by that point you had already made it an empty filesystem.

Can't really tell anything about any disk contents since the diagnostics were taken without the array started.

Start the array in normal mode and post new diagnostics.

Wish you had asked for advice before doing anything at all.

Probably Unraid can't do anything to recover files from those empty disks. If the data was very important, something such as UFS Explorer might be able to recover something.

Do you have backups of anything important and irreplaceable? Parity is not a substitute for backups. Plenty of more common ways to lose data besides a failed disk, including user error.

4 minutes ago, trurl said:

Your cache drive is logging media errors. You should run an extended SMART test on it.

I recommend going into Settings and disabling Docker until you get this fixed.

sorry - diagnostics with array started

walserv-diagnostics-20250824-1949.zip

Edited August 24, 2025Aug 24 by Sponer

Those confirm what you already knew, that disk4 is empty.

Did you tell it to format the disk? Format is NEVER part of rebuild.

11 hours ago, Sponer said:

i have original disk but its empty

How do you know the original disk is empty?

i connect it and use "unnasigned devices" and mount a root share to view the contents

I don't have anything to add that I haven't already said above.