Date of Original Version

10-2012

Type

Conference Proceeding

Rights Management

© 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Abstract or Description

With the continued scaling of NAND flash and multi-level cell technology, flash-based storage has gained widespread use in systems ranging from mobile platforms to enterprise servers. However, the robustness of NAND flash cells is an increasing concern, especially at nanometer-regime process geometries. NAND flash memory bit error rate increases exponentially with the number of program/erase cycles. Stronger error correcting codes (ECC) can be used to tolerate higher errorrates, but these have diminishing returns with increasing P/E cycles and can have prohibitively high power, area, and latency overheads. The goal of this paper is to develop new techniques that can tolerate high bit error rates without requiring prohibitively strong ECC. Our techniques, called FlashCorrect-and-Refresh (FCR) exploit the observation that the dominant error source in NAND flashmemory is retention errors, caused by flash cells losing charge over time. The key idea is to periodically read, correct, and reprogram (in-place) or remap the stored data before it accumulates more retention errors than can be corrected by simple ECC. Detailed simulations of a solid-state drive (SSD) storage system driven by measured experimental data from error characterization on real flashmemory chips show that our techniques provide 46× average lifetime improvement on a variety of workloads at no additional hardware cost. We also find that our techniques achieve lifetimeimprovements that cannot feasibly be achieved with stronger ECC.

DOI

10.1109/ICCD.2012.6378623

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Published In

Proceedings of the IEEE International Conference on Computer Design (ICCD), 2012, 94-101.