提前垃圾回收：改善多通道固態硬碟內部平行度之技術

Abstract

Solid-state disks use multichannel architectures to boost their data transfer rates. Because realistic disk workloads have numerous small write requests, modern flash-storage devices adopt a write buffer and a set of independent channels for better parallelism in serving small write requests. When a channel is undergoing garbage collection, it stops responding to inbound write traffic and accumulates page data in the write buffer. This results in contention for the buffer space and creates idle periods in channels. This study presents a channel management strategy, called garbage-collection forwarding, to utilize idle channel cycles with garbage collection and restore the balance of buffer-space utilization among channels. The key idea is to increase the overlap among garbage-collection activities in different channels. This study further introduces cycle fling, which is a version of garbage-collection forwarding tailored for the operation model of flash planes. Both techniques are compatible with hybrid mapping and page-level mapping. Experimental results show that the proposed methods greatly outperformed existing designs of multichannel systems in terms of the average number of write requests completed per second (IOPS). We also successfully implemented the proposed methods in a real solid-state disk and proved their feasibility in real hardware.

Solid-state disks use multichannel architectures to boost their data transfer rates. Because realistic disk workloads have numerous small write requests, modern flash-storage devices adopt a write buffer and a set of independent channels for better parallelism in serving small write requests. When a channel is undergoing garbage collection, it stops responding to inbound write traffic and accumulates page data in the write buffer. This results in contention for the buffer space and creates idle periods in channels. This study presents a channel management strategy, called garbage-collection forwarding, to utilize idle channel cycles with garbage collection and restore the balance of buffer-space utilization among channels. The key idea is to increase the overlap among garbage-collection activities in different channels. This study further introduces cycle fling, which is a version of garbage-collection forwarding tailored for the operation model of flash planes. Both techniques are compatible with hybrid mapping and page-level mapping. Experimental results show that the proposed methods greatly outperformed existing designs of multichannel systems in terms of the average number of write requests completed per second (IOPS). We also successfully implemented the proposed methods in a real solid-state disk and proved their feasibility in real hardware.