Parity management scheme for a hybrid-storage RAID
Jen-Wei Hsieh, Che-Jen Su · 2016
Recently, the notion of RAID technique has been adopted in SSD-based storage systems to improve the system reliability. However, directly applying RAID technique over SSD's would incur performance degradation due to the out-place-update nature of flash memory. Although using NVRAM as the partial parity cache could alleviate the overhead of frequent parity updates, the contribution of the partial parity cache is confined by its limited size. Some researchers proposed to use an dedicated HDD to store parity data for SSD-based RAID. However, the performance of SSD-based RAID is deteriorated by the inherent overhead of HDD, i.e., seek time and rotation latency. In this paper, we propose a parity management scheme that adopts NVRAM as partial parity cache and uses HDD as parity buffer. With proper management, the performance degradation due to limited cache size can be avoided, while the inherent overhead of HDD can be hidden. The experiment results showed that the proposed PMS-RAID could achieve up to 51.7% improvement in write throughput and up to 47.1% improvement in total block erasures, compared with RAID-5S.