Accelerating enterprise solid-state disks with non-volatile merge caching

Flash memory is now widely used in the design of solid-state disks (SSDs) as they are able to sustain significantly higher I/O rates than even high-performance hard disks, while using significantly less power. These characteristics make SSDs especially attractive for use in enterprise storage systems, and it is predicted that the use of SSDs will save 58,000 MWh/year by 2013. However, Flash-based SSDs are unable to reach peak performance on common enterprise data patterns such as log-file and metadata updates due to slow write speeds (an order-of-magnitude slower than reads) and the inability to do in-place updates. In this paper, we utilize an auxiliary, byte-addressable, non-volatile memory to design a general purpose merge cache that significantly improves write performance. We also utilize simple read policies that further improve the performance of the SSD without adding significant overhead. Together, these policies reduce the average response time by more than 75%, making it possible to meet performance requirements with fewer drives.