6533b821fe1ef96bd127c0c3

RESEARCH PRODUCT

FADaC

subject

description

Solid state drives (SSDs) implement a log-structured write pattern, where obsolete data remains stored on flash pages until the flash translation layer (FTL) erases them. erase() operations, however, cannot erase a single page, but target entire flash blocks. Since these victim blocks typically store a mix of valid and obsolete pages, FTLs have to copy the valid data to a new block before issuing an erase() operation. This process therefore increases the latencies of concurrent I/Os and reduces the lifetime of flash memory. Data classification schemes identify data pages with similar update frequencies and group them together. FTLs can use this grouping to design garbage collection strategies to find victim blocks that have less valid data with respect to having no data classification, and therefore to significantly reduce the number of additional I/Os. Previous data classification algorithms have been designed without leveraging special features of flash memory and often rely on workload-specific configurations. Our classifier FADaC tunes its parameters online and operates on any given amount of memory by storing additional information within the metadata of flash pages. Additional read() requests for the classification are so few that FADaC reduces the internal flash overhead by up to 45% compared to the best classifier from previous work.