I noticed the e-mail alerts about my backups were a lot smaller than they should be, sure enough there was a problem. Logged into my server, and the prognosis was bad.
chris@sandman:~$ ls /backup/ ls: reading directory /backup/: Input/output error chris@sandman:~$ sudo umount /backup/ chris@sandman:~$ sudo mount /backup/ mount: /dev/hdb1: can't read superblock chris@sandman:~$ sudo xfs_check /dev/hdb1 xfs_check: /dev/hdb1 is invalid (cannot read first 512 bytes)
By this time I was very worried, decided rather than mess around anymore I would try a reboot and see what became of that. It would appear either the kernel got confused or the IDE controller decided to sulk. a reboot solved it. 
