A Graph-based Admission Policy for SSD Caching

SSD has been widely used in the cache layer of cloud storage systems to speed up data access. However, existing cache algorithms focus exclusively on performance improvements and ignore the write endurance of SSD, which brings a great challenge to SSD's lifetime. To address this challenge, we analyze some actual workloads and find that most of SSD write operations are unnecessary, such as the data of periodic backup operations. To avoid these unnecessary write operations, we propose a graph-based admission policy for SSD cache, and design analysis engine to facilitate the policy. In the analysis engine, we quantify the correlation strength between blocks, and further propose the Block Rank algorithm for block importance analysis. We measure the activity of the block by introducing the block importance analysis. Experimental results show that the graph-based cache admission policy greatly reduces SSD write traffic. Taking LRU for instance, although hit rate reduces by 1%similar to 2%, SSD write traffic is decreased by 14%similar to 32% in return.