Both drives fail (according to dmesg) but only one is faulty.

[kalpana]

I have a couple of standard SATA drives connected to an Ubuntu box via a Yottermaster 5-bay JBOD array. Recently, while both drives were mounted fine at boot, inside 2 minutes they both showed IO errors.

Thinking it's unlikely (except power surge etc (which I've not had)) for both drives to fail at the same time, I suspected the Yottermaster and / or the cable. Having tested the same drives in another Yottermaster and with a different cable, same results: both drives failed after about 2 minutes. So it must be the drives.

Again - I didn't think both drives could fail at the same time but that's what dmesg was showing me: errors on /dev/sdm and /dev/sdl. So I booted with just one of them in the array. For 24 hours now - no errors whatsoever. Then did the same with the other drive. The second drive reported errors immediately. So it must be that when both drives were installed, the bad drive was somehow affecting the dmesg output and showing both drives failing. I've never seen this behaviour before.

Is there anything I could have done to avoid this? As there were only 2 drives in the 5-bay array (i.e. 3 empty bays) - it was comparatively easy to identify this - but had all 5 bays been full - and only one disk was bad - it would have been much more time consuming to identify the bad drive.
Thanks R