Data associated with the state of a parity update operation in a disk
array system such as a RAID-6 system is stored during performance of the
operation so that, in the event the operation is interrupted, recovery
may be initiated using the stored data. The stored data may include a
state indicator that is indicative of the status of the parity update
operation, and snapshot data (e.g., a delta value indicative of a
difference between new and old data) captured during the parity update
operation.