Abstract
Solid-State Drives (SSDs) offer significant performance improvements over hard disk drives (HDD) on a number of workloads. The frequency of garbage collection (GC) activity is directly correlated with the pattern, frequency, and volume of write requests, and scheduling of GC is controlled by logic internal to the SSD. SSDs can exhibit significant performance degradations when garbage collection (GC) conflicts with an ongoing I/O request stream. When using SSDs in a RAID array, the lack of coordination of the local GC processes amplifies these performance degradations. No RAID controller or SSD available today has the technology to overcome this limitation.
In our previous work, we presented a Global Garbage Collection (GGC) mechanism to improve response times and reduce performance variability for a RAID array of SSDs. A coordination method is employed so that GCs in the array can run at the same time. The coordination can exhibit substantial performance improvement. In this paper, we explore various GC coordination algorithms. We develop reactive and proactive GC coordination algorithms and evaluate their I/O performance and block erase counts for various workloads. We show that a proactive GC coordination algorithm can improve the I/O response times by up to 9% further and increase the lifetime of SSDs by reducing the number of block erase counts by up to 79% compared to a reactive algorithm.
