I recently purchased a HDD and wanted to test for early failure, but no matter how many times I try to preclear the drive it keeps coming back with FAIL! Invalid Unraids MBR signature on 3ZGYASGZ (sdk). I'm using the latest version of the Unassigned Devices Preclear plugin (2028.08.20). The first time I tried preclearing I was using a USB dock and thought there might be an issue with the dock, so I tried putting the HDD in my server and rebooting it instead but I'm still running into this issue. This is being connected via Dell PERC H310 to a supermicro 16 bay SAS2 backplane.

This seems to happen right after it finishes zeroing the drives.

unnas-diagnostics-20250903-2129.zippreclear.txt

Edited September 4, 2025Sep 4 by bobokun

You can just add the drive to the array and let Unraid clear it, if that doesn't fail, it would be a plugin issue.

I don’t plan on using this drive right away. It’s meant as a backup ready to be replaced in case a drive fails. Is there anyway Unraid can preclear it and have it ready without adding it to the array?

Unraid can only clear, not preclear, recommend you post in the support thread for the plugin you are using, could be an issue with the drive size, though that seems unlikely.

If I add it to the array and let it clear the disk but don't format after, instead just stop the array and remove the disk, would that be considered "precleared" and would parity be valid still after removing the disk?

That should work, but you will need to do a new config (tools - new config) to remove the disk, but if done before formatting it, you can check "parity is already valid".

Note that I never tested the above, so I'm not sure the drive keeps the cleared signature. Also,

2 hours ago, bobokun said:

It’s meant as a backup ready to be replaced in case a drive fails

Drives don't need to be cleared to be used as replacements, only when adding as a new array disk.