A design to reduce write amplification in object-based NAND flash devices

Abstract

Write amplification is a major cause of performance and endurance degradations in NAND flash based storage systems. In an object-based NAND flash device, two causes of write amplification are onode partial update and cascading update. Updating one onode, a kind of small-sized object metadata, invokes partial page update (i.e., onode partial update) that incurs unnecessary migration of the un-updated data. An cascading update denotes that object metadata is updated in a cascading manner due to erase-before-program property of NAND flash memory. In this work, we propose a system design to alleviate onode partial update and cascading update. The proposed system design includes: 1) A multi-level garbage collection technique to minimize unnecessary data migration incurred by onode partial update; 2) A B+ table tree and selective cache design to reduce the write operations associated with cascading update; and 3) A power failure handling technique to guarantee system consistency. Experiment results show that our proposed design can achieve up to 20% write reduction compared to the best state-of-the-art.