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 systems. It is desirable to have disk arrays and clustered storage systems with higher data redundancy, such as RAID-6. Meanwhile, latest research also indicates disk sector failures occur much more often than whole disk failures. It is hence important to study efficient disk sector failure recovery schemes for RAID-6. This paper studies how to efficiently recover disk sector 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 erasure decoding algorithm SCAN is derived from these conditions. 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 analysis show SCAN outperforms Matrix Method in all the relevant 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.