The Research On Partial Elastic Stripe Technique Based On Flash RAID

With the popularity of Solid State Drives(SSD),SSDs are gradually replacing Disks to be the main storage device.At the same time,Redundant Array of Independent SSDs(RAIS)is also widely used.However the critical small-write problem on RAIS5,including readmodify-write(RMW)and read-reconstruct-write(RCW),degrades RAIS5's writing performance and causes unbalance lifetime between data blocks and parity blocks which extremely affects its reliability.Aiming at the small-write performance and the lifetime of RAIS5,we designed a Partial Elastic-RAIS5(PE-RAIS)system based on origin RAIS5 system to optimize the small-write performance of RAIS5 and balance the wear of data blocks and parity blocks on array level to extend lifetime.PE-RAIS5 combines the parity caching technique and elastic striping technique,and proposes the Partial Elastic Strip Strategy which uses dynamic address mapping and static address mapping both for reducing metadata overhead in elastic striping technique.First PE-RAIS5 uses data cache to aggregate write data,so hot data just need to be replaced in data cache.Then PE-RAIS5 applys Partial Elastic Strip Strategy to reconstruct new full-written stripes with updated data blocks from non-fullwritten stripes which were swapped out from the data cache which is called dynamic address mapping and needs stripe metadata to keep the address mapping information.And for fullwritten stripes,PE-RAIS5 trys to adopte traditional RAIS5 address mapping method which is called static address mapping to reduce the cost of metadata.PE-RAIS5 improves smallwriting performance by reducing small writes and parity updates.PE-RAIS5 also increases RAIS5's lifetime by the wear-leveling between data blocks and parity blocks on system level.After several experimental tests,compareing to RAIS5,PE-RAIS5 shows better write performance in the scene with quite a lot of small-writes and similar write performance in the scene with few small-writes.