FSAF - FILE SYSTEM AWARE FLASH TRANSLATION LAYER F…….ppt

Thank You! * * * * * * * * * A Superblock-based Flash Translation Layer for NAND Flash Memory S K Mylavarapu*, A Shrivastava*, J-E Lee*, S Choudhuri^ and Tony Givargis^ *Arizona State University ^University of California, Irvine C M L Popularity of Flash Memories What is Flash? A non-volatile computer memory that can be electrically erased and reprogrammed Belongs to EEPROM family Where is it used? Where mobility, power, speed, and size are key factors! Flash is ubiquitous! How about its Market? NAND flash markets have more than tripled from $5 billion in 2004 to $18 billion in 2009. Flash and Memory Hierarchy Higher Speed, Cost Larger Size Flash is faster, more robust, but expensive than hard disks Some works proposed NAND flash for RAM Flash at Work Erase before rewrite! Once a flash cell is programmed, a whole block of cells needs to be erased before it can be reprogrammed. In order to reduce the erasure overhead, erasures are done on a group of cells – called a Block For faster reads and writes, Blocks are subdivided into smaller granularity Pages Each page update results in a Block erasure ! Extremely time consuming – increases page write time by an order Results in faster Flash wear  Default State: ERASED PROGRAMMED Flash at Work Flash is organized as Primary and Replacement Blocks. Replacement blocks serve as (re-)write log buffers, to hide Erase before rewrite limitation. A Fold occurs when a re-write is issued to a block with full replacement block Consolidate valid data into one new block As the free space in the device falls below a critical threshold, free space needs to be generated by performing a series of Folds Garbage Collection (GC) - a series of folds Unpredictable and Long, depending upon data distribution Some blocks may be erased (wear) more than others A single block failure may lead to the whole device’s failure Wear Leveling (WL) – a regular operation to balance block wear GC and WL operations determine application respon