GC-Steering: GC-aware Request Steering and Parallel Reconstruction Optimizations for SSD-based RAIDs

Solid-state disk (SSD)-based redundant array of independent disks (RAIDs) have been widely deployed in high-end enterprize systems to provide high-performance and highly reliable storage for data-intensive computing. However, SSD-based RAIDs suffer from significant performance degradation whenever user I/O requests conflict with the ongoing garbage collection (GC) operations which introduce tail latency. Moreover, the performance characteristics of SSDs make the traditional HDD-based RAID reconstruction algorithms are not compatible with or suitable for SSD-based RAIDs. In this article, we proposed GC-aware request steering (GC-Steering), a scheme aware of the GC process within an SSD-based RAID, to significantly boost the performance and reliability of SSD-based RAIDs. GC-Steering effectively outsources the popular read requests and all write requests addressed to the SSD currently in the GC state to a staging space, such as a dedicated spare SSD or the reserved space of each SSD within the RAID. GC-Steering also accelerates the performance of the failure-recovery process by both request steering and parallel recovery. Our extensive evaluations on a lightweight GC-Steering prototype driven by HPC-like and real-world enterprize workloads show that the GC-Steering scheme significantly reduces the average response time by an average of 63.3% and 65.8%, compared with the state-of-the-art local GC and global GC schemes. Moreover, the GC-Steering scheme also significantly reduces the average response times by an average of 62.3% during RAID reconstruction than the normal state.