Revitalizing Copybacks in Modern SSDs: Why and How

TL;DR

This paper introduces rCopyback, a restricted copyback method for SSDs that improves performance by limiting consecutive copybacks to ensure data reliability, and an rCopyback-aware FTL that optimizes its use based on workload.

Contribution

It proposes rCopyback, a novel limited copyback technique, and an rCopyback-aware FTL that intelligently manages internal data migrations for better SSD performance.

Findings

rCopyback improves SSD performance by limiting consecutive copybacks.

rcFTL intelligently decides when to use rCopyback, optimizing throughput.

Average I/O throughput increases by 54% with rcFTL.

Abstract

For modern flash-based SSDs, the performance overhead of internal data migrations is dominated by the data transfer time, not by the flash program time as in old SSDs. In order to mitigate the performance impact of data migrations, we propose rCopyback, a restricted version of copyback. Rcopyback works like the original copyback except that only n consecutive copybacks are allowed. By limiting the number of successive copybacks, it guarantees that no data reliability problem occurs when data is internally migrated using rCopyback. In order to take a full advantage of rCopyback, we developed a rCopyback-aware FTL, rcFTL, which intelligently decides whether rCopyback should be used or not by exploiting varying host workloads. Our evaluation results show that rcFTL can improve the overall I/O throughput by 54% on average over an existing FTL which does not use copybacks.