Tonight I was unable to copy a file to my array. When I checked the server, I had two drives offline, and there were 7 or 8 drives showing errors. I rebooted and when it restarted a 3rd drive was shown as missing, along with the other two offline.

This is a problem I've experienced randomly throughout the many years that I have been using Unraid. My system will work flawlessly for many months and then out of the blue some number of drives will show errors and go offline. The number of errors can be as low as a few dozen or tens or hundreds of thousands of errors. Sometimes only the offline drives show errors, in other cases additional drives show errors but are not offline.

My drives are located in a tower case where some drives are connected to motherboard SATA connectors plus an LSI HBA. Additional drives are located in a cheap external 8-bay drive enclosure connected to another LSI HBA card. The most recent errors have occurred in the external enclosure. Trying to solve the problems, I have replaced the HBA, the cables to the enclosure, and the internal breakout cables. The only thing I haven't changed is the mini-SAS pass-through connector on the enclosure because I haven't been able to find a compatible replacement.

Every time I've had drives go offline, I have never been able to find any problems with the offline drives. I usually just replace the drives and rebuild without issue. In a few cases I've had to recreate the parity disks and then copy files from the "failed" drives. Fortunately, I haven't lost any data. (Yes, I know I should have a true backup, until recently I haven't had the means to build a backup box, but I am working on it.)

Any tips for tracking down the cause and preventing it in the future?

unbucket-diagnostics-20251201-2306.zip

Diags are after rebooting, so we can't see what happened, if it happens again, post the diags before rebooting.