OI-RAID: A Two-Layer RAID Architecture towards Fast Recovery and High Reliability

A lot of inexpensive disks in modern storage systems induce frequent disk failures. It takes a long time to recover a failed disk due to its large capacity and limited I/O. This paper proposes a hierarchical architecture of erasure code, OI-RAID. OI-RAID consists of two layers of codes, outer layer code and inner layer code. The outer layer code is based on disk grouping and Balanced Incomplete Block Design (BIBD) with skewed data layout to provide efficient parallel I/O of all disks for failure recovery. Inner layer code is deployed within a group of disks. As an example, we deploy RAID5 in both layers and present detailed performance analysis. With RAID5 in both layers, OI-RAID tolerates at least three disk failures meeting practical data availability, and achieves much higher speed up of disk failure recovery than existing approaches, while keeping optimal data update complexity and practically low storage overhead.