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 buffer space and creates idle periods in channels. This study presents a channel-management strategy, called garbage-collection advancing, which allows early start of garbage collection in channels for increasing the overlap among channel activities of garbage collection and restoring the balance of buffer-space usage among channels. This study further introduces cycle filling, which is a version of garbage-collection advancing tailored for the operation model of flash planes. Experimental results show that the proposed methods greatly outperformed existing designs of multichannel systems in terms of response and throughput. We also successfully implemented the proposed methods in a real solid-state disk and proved their feasibility in real hardware. ACM Reference Format:Li-Pin Chang and Chen-Yi Wen. 2013. Reducing asynchrony in channel garbage-collection for improving internal parallelism of multichannel solid-state disks.
Solid-state disks use arrays of flash-memory chips for data storage. They adopt multichannel architectures to exploit parallelism among flash operations. Under real disk workloads, a channel spends nearly the same amount of time on writing host data and collecting garbage. Thus, the key to the success of multichannel architectures is to achieve high parallelism among channel operations under these two kinds of activities. This study presents a channel management scheme that comprises a write-buffer design and two channel management policies. The proposed scheme is designed to be generic, and it is applicable to both hybrid mapping and page-level mapping. Our experimental results show that the proposed management scheme doubles the average number of write requests completed per second (e.g., write IOPS) of a baseline multichannel architecture. We also successfully implemented the proposed scheme in a real solidstate disk and demonstrated the feasibility of our approach.
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