Crash Recovery in FAST FTL

Abstract

NAND flash memory is one of the non-volatile memories and has been replacing hard disk in various storage markets from mobile devices, PC/Laptop computers, even to enterprise servers. However, flash memory does not allow in-place-update, and thus a block should be erased before overwriting the existing data in it. In order to overcome the performance problem from this intrinsic deficiency, flash storage devices are equipped with the software module, called FTL (Flash Translation Layer). Meanwhile, flash storage devices are subject to failure and thus should be able to recover metadata (including address mapping information) as well as data from the crash. In general, the FTL layer is responsible for the crash recovery. In this paper, we propose a novel crash recovery scheme for FAST, a hybrid address mapping FTL. It writes periodically newly generated address mapping information in a log structured way, but it exploits the characteristics of FAST FTL that the log blocks in a log area are used in a round-robin way, thus providing two advantages over the existing FTL recovery schemes. One is the low overhead in performing logging during normal operations in FTL. The other is the fast recovery time.