Towards higher disk head utilization: extracting free bandwidth from busy disk drives

Freeblock scheduling is a new approach to utilizing more of a disk's potential media bandwidth. By lling rotational latency periods with useful media transfers, 20{50 % of a never-idle disk's bandwidth can often be provided to background applications with no eect on foreground response times. This paper describes freeblock scheduling and demon-strates its value with simulation studies of two con-crete applications: segment cleaning and data min-ing. Free segment cleaning often allows an LFS le system to maintain its ideal write performance when cleaning overheads would otherwise reduce perfor-mance by up to a factor of three. Free data mining can achieve over 47 full disk scans per day on an active transaction processing system, with no eect on its disk performance.