SCAN: An Efficient Sector Failure Recovery Algorithm for RAID-6 Codes

Recent studies show disks fail much more often in real systems than specified in their data-sheets and RAID-5 may not be able to provide needed reliability for practical sys-tems. It is desirable to have disk arrays and clustered stor-age systems with higher data redundancy, such as RAID-6. Meanwhile, latest research also indicates disk sector fail-ures occur much more often than whole disk failures. It is hence important to study efficient disk sector failure recov-ery schemes for RAID-6. This paper studies how to efficiently recover disk sec-tor failures for RAID-6 codes. First for most well known RAID-6 codes, we provide the conditions to determine the recoverability of their erasure patterns. Then a generic era-sure decoding algorithm SCAN is derived from these con-ditions. SCAN is able to recover both sector and whole disk failures, like Matrix Method, but SCAN is much more efficient in time complexity. Extensive simulations and anal-ysis show SCAN outperforms Matrix Method in all the rel-evant decoding performance metrics. Therefore, SCAN is an attractive decoding algorithm to be integrated into these systems using RAID-6 codes, like disk arrays or clustered storage systems.