VSSD: Performance Isolation in a Solid-State Drive

Performance isolation is critical in shared storage systems, a popular storage solution. In a shared storage system, interference between requests from different users can affect the accuracy of I/O cost accounting, resulting in poor performance isolation. Recently, NAND flash-memory-based solid-state drives (SSDs) have been increasingly used in shared storage systems. However, interference in SSD-based shared storage systems has not been addressed. In this article, two types of interference, namely, queuing delay (QD) interference and garbage collection (GC) interference, are identified in a shared SSD. Additionally, a framework called VSSD is proposed to address these types of interference. VSSD is composed of two components: the FACO credit-based I/O scheduler designed to address QD interference and the ViSA flash translation layer designed to address GC interference. The VSSD framework aims to be implemented in the firmware running on an SSD controller. With VSSD, interference in an SSD can be eliminated and performance isolation can be ensured. Both synthetic and application workloads are used to evaluate the effectiveness of the proposed VSSD framework. The performance results show the following. First, QD and GC interference exists and can result in poor performance isolation between users on SSD-based shared storage systems. Second, VSSD is effective in eliminating the interference and achieving performance isolation between users. Third, the overhead of VSSD is insignificant.