LTFTL: Lightweight time-shift Flash Translation Layer for Flash memory based embedded storage

Abstract

Flash memory storage has been widely used in various embedded systems such as digital cameras, MP3 players, cellular phones, and DMB devices and now it applies to PCs as a form of SSDs. Characteristics of Flash memory necessitate a software layer called FTL (Flash Translation Layer) that directs modified data to new places in Flash memory and maintains a mapping between a logical sector number to a physical page. We notice that this out-of-place update scheme of the FTL allows a low-overhead time-shifting between multiple versions of storage state. From this observation, we propose LTFTL (Lightweight Time-shift FTL) that provides not only multiple versions of storage state but also an open-ended interface to traverse them. This open-ended interface can be used to support fault-resilience schemes, transactions of various granularities, and user-friendly roll-back services. Experimental results from a prototype implementation show that the proposed LTFTL can (1) provide a low-overhead time-shift capability at the user level by maintaining multiple storage states and (2) enhance the reliability/survivability of Flash memory by allowing to roll back to a previous consistent storage state at the storage system level.