Container Marking: Combining Data Placement, Garbage Collection and Wear Levelling for Flash

This paper presents a data-placement scheme for log-structured flash translation layers (FTLs), with the dual aims of reducing write amplification due to garbage collection and flash wear-out due to block erasing and programming. The central idea is to identify and place data that is expected to change frequently together in young flash blocks that are far from wearing out, and infrequently changing data in old blocks where it can be expected to stay longer. In previous work, garbage collection and wear levelling were treated separately, and the importance of data placement was largely ignored. We propose a new scheme, called container marking, to combine data placement, garbage collection, and wear levelling in a single mechanism, thus improving both the random write performance and the endurance. Each flash block is a data container that is assigned an activeness marker indicating how frequently the data it stores is updated. A simple solution for dynamically tracking data's activeness that adapts to utilizations is presented. The system is implemented in a Java1-based flash simulator, and is shown to reduce write amplification and wear-out in synthetic and trace-driven workloads.