Data Allocation Algorithm based on Write and Read Frequency for Double Asymmetric-latency SCM SSD

Storage class memories (SCMs) realize fast access latency. However, SCMs have a trade-off between reliability and latency in case of correcting errors. To achieve high reliability and high performance, double asymmetric-latency SCM SSD has been proposed. Previously proposed SSD consists of fast-write/slow-read SCM (W-SCM) and fast-read/slow-write SCM (R-SCM). W-SCM and R-SCM are realized by changing strength of ECC and number of Set/Reset verify cycles by SSD controller. Previously proposed SSD with asymmetric read/write latency requires frequently written (write-hot) data to be allocated in W-SCM and frequently read (read-hot) data to be allocated in R-SCM to achieve high performance [1]. Conventional data allocation algorithm for previously proposed SSD [1] triggers frequently data movement and degrades SSD performance. Therefore, this paper proposes data allocation algorithm that restricts data movement and stores write-hot, read-hot and cold data separately in W-SCM and R-SCM based on access frequency. As a result, SSD performance is improved by 14.1% for write-hot workload and 67.7% for read-hot workload compared to conventional algorithm.