Code 5-6: An Efficient MDS Array Coding Scheme to Accelerate Online RAID Level Migration

Abstract

With the rapid growth of data storage, the demand for high reliability becomes critical in large data centers where RAID-5 is widely used. However, the disk failure rate increases sharply after some usage, and thus concurrent disk failures are not rare, therefore RAID-5 is insufficient to provide high reliability. A solution is to convert an existing RAID-5 to a RAID-6 (a type of "RAID level migration") to tolerate more concurrent disk failures via erasure codes, but existing approaches involve complex conversion process and high transformation cost. To address these challenges, we propose a novel MDS code, called "Code 5-6", to combine a new dedicated parity column with the original RAID-5 layout. Code 5-6 not only accelerates online conversion from a RAID-5 to a RAID-6, but also demonstrates several optimal properties of MDS codes. Our mathematical analysis shows that, compared to existing MDS codes, Code 5-6 reduces new parities, decreases the total I/O operations, and speeds up the conversion process by up to 80%, 48.5%, and 3.38×, respectively.