I had a drive drop out of the array today and become disabled. There doesn't appear to be anything wrong with it from that I can tell. Stopped the array, restarted it, same. Stopped the array, pulled (hot plug) the drive out, reinserted it, restarted the array, same. Several reboots, same.

Diagnostics attached.

backuptower-diagnostics-20260124-2314.zip

SMART for disk13 looks OK, and emulated disk13 is mounted.

21 minutes ago, ashman70 said:

Several reboots

Since you rebooted, can't tell what happened before, so don't know why it was disabled. Possibly connection problem.

Check connections. Should be OK to rebuild to the same disk.

https://docs.unraid.net/unraid-os/using-unraid-to/manage-storage/array/replacing-disks-in-array/#re-enabling-a-disabled-disk-rebuilding-onto-itself

Unraid disables a drive as soon as a write to it fails whatever the reason as it is no longer in sync with parity. Connection or power problems are far more common than actual disk problems.

The syslog in the diagnostics is the RAM version that starts afresh every time the system is booted.

If this keeps happening then you should enable the syslog server (probably with the option to Mirror to Flash set) to get a syslog that survives a reboot so we can see what leads up to the problem. The mirror to flash option is the easiest to set up (and if used the file is then automatically included in any diagnostics), but if you are worried about excessive wear on the flash drive you can put your server's address into the remote server field and log to a share instead.