An empirical study of redundant array of independent solid-state drives (RAIS)

Solid-state drives (SSD) are popular storage media devices alongside magnetic hard disk drives (HDD). SSD flash chips are packaged in HDD form factors and SSDs are compatible with regular HDD device drivers and I/O buses. This compatibility allows easy replacement of individual HDDs with SSDs in existing storage systems. However, under certain circumstances, SSD write performance can be significantly slowed by garbage collection (GC) processes. The frequency of GC activity is directly correlated with the frequency of inside-SSD write operations and the amount of data written to it. GC scheduling is locally controlled by an internal SSD logic. This paper studies the feasibility of Redundant Arrays of Independent Flash-based Solid-state drives (RAIS). We empirically analyze the RAIS performance using commercially-off-the-shelf (COTS) SSDs. We investigate the performance of various RAIS configurations under a variety of I/O access patterns. Finally, we present our performance and cost comparisons of RAIS with a fast, PCIe-based COTS SSD, in terms of performance and cost.