fstab drive auto-mounted to wrong (non-existent) dev

Question

I ran into a curious problem today.

ls /media/Personal would yield ls: reading directory .: Input/output error.

According to mount, that folder was mounted from /dev/sdb1. Yet according to blkid, I only had drives on sda1 and sdc1.

umounting it (resulted in segmentation fault but was successful),
then running mount -t ext4 /dev/sda1 /media/Personal brought everything back to normal.

The question is, how could this have possibly happened in the first place? No manual mounts were performed since boot (really, not much of anything was done since boot), and fstab is as follows:

UUID=0119497c-ae50-42e0-9015-e557bf71398e /media/Business ext4 defaults,nofail 0 0
UUID=a36fd062-5cbf-4e4b-abd5-926f84287cf9 /media/Personal ext4 defaults,nofail 0 0

It's certainly odd that I ended up with sdc and not sdb. Moreso, there was nothing wrong with the "Business" mount (same type of drive, no SMART errors on either). This is on Raspbian Jessie.

Answer 1

Raspbian? So the drives are connected via USB probably.

My guess is the drive had been registered as /dev/sdb and mounted as it should. Then there was something like power fluctuation that caused the drive to go offline and online right after, but as /dev/sdc this time. The old, nonexistent device remained formally mounted.

I made a test in my Kubuntu. I recreated this scenario with my first try, no sweat. I got Input/output error but no segmentation fault. I suppose Kubuntu handles such situations more gracefully, hence the difference.

There is one thing that bothers me though. You claim you had to manually mount /dev/sda1 to set things right afterwards. In my scenario /dev/sda1 would be the other (unaffected) drive and you should have mounted /dev/sdc1. For now I cannot explain how you could have your drive mounted as nonexistent /dev/sdb1, still available as /dev/sda1, while the other drive apparently being /dev/sdc1 from the very beginning (mounted all the time without issues).

So this answer can't fully explain what happened in your case (unless you made a typo and it was /dev/sdc1 you had mounted by command). Nevertheless the answer may be useful for future users with similar problem.