Transaction failure: occurs when it fails to execute or when it reaches a point from where it can't go any further.
Logical errors: transaction cannot complete due to some internal error condition.
System errors: the database system must terminate an active transaction due to an error condition (e.g., deadlock)
System crash: a power failure or other hardware or software failure causes the system to crash.
Fail-stop assumption: non-volatile storage contents are assumed to not be corrupted as result of a system crash Database systems have numerous integrity checks to prevent corruption of disk data.
Disk failure: a head crash or similar disk failure destroys all or part of disk storage Destruction is assumed to be detectable: disk drives use checksums to detect failures.