SSD Assisted Caching for Restore Optimization in Distributed Deduplication Environment

Better deduplication performance often leads to degraded restore performance because it causes higher fragmentation. Unlimited amount of available memory or high locality of deduplicated data are ideal for the best restore performance. But both of them are not practical in the real world. As a result, restore performance needs to be optimized either through strengthening locality by selective re-writing and/or making the best use of the limited available memory through cache optimization. In this paper, we explore SACRO, SSD Assitsted Caching for Restore Optimization in distributed deduplication environment, which avoids the need to repetitively access chunk containers in disk by using SSD(Solid State Drives) as a secondary chunk cache. An FRT(Future Reference Table) is constructed from the recipe of a backup stream before the actual restore is started and an FRC(Future Reference Count) entry in the FRT is utilized to assign priorities to chunks as they are accessed during restoration. These priority values coupled with access distances are used to decide to cache a chunk either in memory or the SSD. The restore performance of SACRO is shown to significantly outperform other restoring approaches which utilize chunk caching. Moreover, SACRO can be integrated to already existing deduplication systems with very limited amount of modification done on the deduplication system.