Hi all, I'm doing a data recovery project with some old tapes, and because the tape drives are SCSI, I have two Adaptec AHA-2940/2940UW SCSI Controller PCI cards. This has been a several months long project involving writing custom drivers and reverse engineering firmware. But, that's not relevant.

But my problem here is about the PCI SCSI adapter. Early on, I had problems with erratic tape drive behavior. Sometimes, the drives would constantly power cycle. Usually it seemed to be during large data transfers, so I could rewind the tape just fine, but when I started to read data it would reset. Other times it would just constantly reset regardless of if the computer would send commands. Eventually I realized that if I unplugged the SCSI PCI card the issues stopped. So, I assumed the card to be defective and ordered another card. It worked great until the same issues started to surface. At this point, I tried another motherboard and was surprised to find that fixed it.

Several months passed without issue until it started happening again. I swapped the motherboard for another one and the issues have gone away again. I do not believe the tape drives to be defective because switching out two tape drives doesn't fix the issue when swapping motherboards generally is best. The issue is erratic too, some reboots it works just fine and others it doesn't. That isn't good enough for me though because (for reasons which would be a deep rabbit hole to dive into), I have to do a LOT of power cycles of the entire machine to dump data from damaged tapes.

What could be a possible explanation for needing to swap motherboards like this?