the majority of our failovers were storage related. For a number of years we were running a RAID before moving to SAN which has been better. The RAID never actually lost data but DID go down: interface card failure, disk failure (yes it's not supposed to but tell that to the equipment-- an electirically malfunctioning drive can interfere with the operation of the overall system), quorum file corruption. The problem is that a shared storage system is a single point of failure, one that can often be avoided with mirroring.