Recently one of our servers has been suffering from file system corruptions. It would be fine under normal circumstances, but under load there was a good chance a corruption would occur within a few minutes.
We're using two Seagate 7200.9 disks in a RAID-1 array and neither were showing any of the usual tell-tale signs of failure, and I've always found Linux software RAID to be rock-solid, so I was starting to suspect the Promise TX2 SATA controller we're using.
It turns out however it was faulty memory. Linux uses spare RAM to cache the file system, and so clearly if your RAM is bad then file system access is going to be affected. I've now replaced the RAM and all is well again.