Optimizing read and write performance based on deep understanding of SSD

Abstract

Flash-based Solid State Drive (SSD) consists of multiple Flash devices, and achieves high I/O bandwidth by parallel data access, buffer schemes and prefetching. Currently, the capacity of high-performance SSD reaches several TBs, and the nominal read/write bandwidth reach GB/s. However, since Flash is accessed in page unit, SSD may have a low performance resonant range when combining specific parameters. Deeply understanding the internal structure of SSD is important for exploiting the parallelism of SSD. Due to the competitions among SSD manufactories, they are reluctant to publish important parameters of their SSD products, which makes it difficult to fully take the advantages of high performance of SSD. This paper analyzes typical SSD internal structure, parallel characteristic, the mapping relationship, and the potential low performance resonant range. It puts forward a technical method to explore the internal structure of SSD. We analyze the average distribution of file sizes, and determine the relationship between minimum size and the bandwidth of read/write requests. We analyze the reason why the size of read/write requests shrink along the processing, and propose mechanisms to prevent the shrinking of read/write request size and to avoid low performance resonant range, for achieving higher read/write performance.