RELIABILITY MODELING OF DECLUSTERED-PARITY RAID CONSIDERING UNCORRECTABLE BIT ERRORS

UNcorrectable Bit Errors (UNBEs) are important in considering the reli ability of Redundant Array of Inexpensive Disks (RAID). They however, have been ignored or have not been studied in detail in existing relia bility analysis of RAID. In this paper. we present an analytic model t o study the reliability of declustered-parity RAID by considering UNBE s. By using the analytic model, the optimistic and the pessimistic est imates of the probability that data loss occurs due to an UNBE during the data reconstruction after a disk failed (we call this DB data loss ) are obtained. Then, the optimistic and the pessimistic estimates of the Mean Time To Data Loss (MTTDL) that take into account both DB data loss and the data loss caused by double independent disk failures (we call this DD data loss) are obtained. Furthermore, how the MTTDL depe nds on the number of units in a parity stripe, rebuild time of a faile d disk and write fraction of data access are studied by numerical anal ysis.