Extending Lifetime of SSD in Raid5 Systems through a Reliable Hierarchical Cache

Abstract

SSD suffer from lifetime problem, particularly when they are deployed in all flash RAID5 systems and work under workload dominated by random updates. To cost- effectively and reliably extend the lifetime of those SSD, we propose a novel reliable hierarchical buffer cache, named RH-cache. RHcache consists of an upper- level write cache built upon a smallsize NVRAM and a lower-level write cache built upon a sub-RAID divided from the underlying SSD RAID. The upper-level write cache merges random updates into sequential writes thus reducing updates on the parity chunks. And the lower- level write cache can reduce the updates on data chunks by exploring content locality in the write workload. A prototype of RH-cache has been built to evaluate its effectiveness and efficiency. Both I/O benchmarks and real-world workloads driven experiments are conducted. The experimental results demonstrate RH-cache can reduce the updates in SSD by up to 80% compared with that without RH-cache.