Cleaning policies in mobile computers using flash memory

Flash memory is small, lightweight, shock-resistant, nonvolatile, and consumes little power. Flash memory therefore shows promise for use in storage devices for consumer electronics, mobile computers and embedded systems. However, flash memory cannot be overwritten unless erased in advance. Erase operations are slow that usually decrease system performance, and consume power. The number of erase cycles is also limited. For power conservation, better system performance, and longer flash memory lifetime, system support for erasure management is necessary. In this paper, we use the non-update-in-place scheme to implement a flash memory server and propose a new cleaning policy to reduce the number of erase operations needed and to evenly wear out flash memory. The policy uses a fine-grained method to effectively cluster hot data and cold data in order to reduce cleaning overhead. A wear-leveling algorithm is also proposed. Performance evaluations show that erase operations are significantly reduced and flash memory is evenly worn, Though the proposed fine-grained separation scheme is targeted at flash memory-based systems, it can be applied to other storage systems as well. (C) 1999 Elsevier Science Inc. All rights reserved.