You may get this after a long time of not rebooting but especially if you have rsync'd a / partition or deployed an image to another VPS or computer, you will often have this issue.
The good thing it usually just takes a reboot.
Here is more info from Centos........
I've got one of these for testing projects from work at home and got more than I bargained for with the time I've spent on it due to the storage handing/Perc 6/i cards.
My particular model came with the following:
2U Rack Mount Server with Rails
2xOpteron 2373 EE (Quad Core, there is a 6-core version that can be found at times)
2 x 250GB Seagate SATA
2 x Dell Perc 6/i (horrible and a nightmare to work........