PLC-cache: Endurable SSD cache for deduplication-based primary storage

Data deduplication techniques improve cost efficiency by dramatically reducing space needs of storage systems. SSD-based data cache has been adopted to remedy the declining I/O performance induced by deduplication operations in the latency-sensitive primary storage. Unfortunately, frequent data updates caused by classical cache algorithms (e.g., FIFO, LRU, and LFU) inevitably slow down SSDs' I/O processing speed while significantly shortening SSDs' lifetime. To address this problem, we propose a new approach-PLC-Cache-to greatly improve the I/O performance as well as write durability of SSDs. PLC-Cache is conducive to amplifying the proportion of the Popular and Long-term Cached (PLC) data, which is infrequently written and kept in SSD cache in a long time period to catalyze cache hits, in an entire SSD written data set. PLC-Cache advocates a two-phase approach. First, non-popular data are ruled out from being written into SSDs. Second, PLC-Cache makes an effort to convert SSD written data into PLC-data as much as possible. Our experimental results based on a practical deduplication system indicate that compared with the existing caching schemes, PLC-Cache shortens data access latency by an average of 23.4%. Importantly, PLC-Cache improves the lifetime of SSD-based caches by reducing the amount of data written to SSDs by a factor of 15.7.