Exploiting Page Correlations for Write Buffering in Page-Mapping Multichannel SSDs

Abstract

Advanced solid-state disks (SSDs) have been equipped with page-mapping flash translation layers and multichannel architectures. The SSDs employ a RAM-based write buffer, which delays write requests for reducing write traffic, reorders requests for mitigating garbage-collection overhead, and produces parallel page writes for improving channel time utilization. This work presents a novel write buffer algorithm that exploits temporal and spatial correlations among buffer pages. The write-buffer groups temporally or spatially correlate buffer pages and then write the grouped buffer pages to the same flash block. In this way, when the correlated page data are updated in the future, flash blocks will receive bulk page invalidations and become good candidates for garbage collection. With multichannel architectures, the write buffer adaptively disperses read-most sequential data over channels for high page-level parallelism of sequential reads, while clustering write-most sequential data in the same channel for a reduced cost of garbage collection. We evaluated the proposed method and previously proposed buffer algorithms. Our method was shown to outperform the existing methods by up to 134%. We also implemented our buffer design on the OpenSSD platform; the time and space overheads of our design were reported to be very low.