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Published April 2018 | public
Journal Article

An Analysis of Flash Page Reuse With WOM Codes

Abstract

Flash memory is prevalent in modern servers and devices. Coupled with the scaling down of flash technology, the popularity of flash memory motivates the search for methods to increase flash reliability and lifetime. Erasures are the dominant cause of flash cell wear, but reducing them is challenging because flash is a write-once medium— memory cells must be erased prior to writing. An approach that has recently received considerable attention relies on write-once memory (WOM) codes, designed to accommodate additional writes on write-once media. However, the techniques proposed for reusing flash pages with WOM codes are limited in their scope. Many focus on the coding theory alone, whereas others suggest FTL designs that are application specific, or not applicable due to their complexity, overheads, or specific constraints of multilevel cell (MLC) flash. This work is the first that addresses all aspects of page reuse within an end-to-end analysis of a general-purpose FTL on MLC flash. We use a hardware evaluation setup to directly measure the short- and long-term effects of page reuse on SSD durability and energy consumption, and show that FTL design must explicitly take them into account. We then provide a detailed analytical model for deriving the optimal garbage collection policy for such FTL designs, and for predicting the benefit from reuse on realistic hardware and workload characteristics.

Additional Information

© 2018 ACM. Received February 2017; revised September 2017; accepted January 2018. This work was supported in part by United States-Israel Binational Science Foundation (BSF) grant 2010075, NSF grant CCF-1218005, Israel Science Foundation (ISF) grant 1624/14, EU Marie Curie Initial Training Network SCALUS grant 238808, and German-Israeli Foundation for Scientific Research and Development (GIF) grant I-1356-407.6/2016. We thank Hila Arobas for her help with the low-level experiments and the anonymous reviewers for their suggestions that helped improve this manuscript.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023