Towards Higher Disk Head Utilization: Extracting "Free" Bandwidth From Busy Disk Drives
Appears in Proc. of the 4th Symposium on Operating Systems Design and Implementation, October 2000. Supercedes CMU SCS Technical Report CMU-CS-00-130, May 2000.
Christopher Lumb, Jiri Schindler, Gregory R. Ganger, Erik Riedel*, David F. Nagle**
Dept. of Electrical and Computer Engineering
School of Computer Science**
Carnegie Mellon University
Pittsburgh, PA 15213
*Seagate Technology, Pgh., PA
Freeblock scheduling is a new approach to utilizing more of a disk's potential media bandwidth. By filling 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 effect on foreground response times. This paper describes freeblock scheduling and demonstrates its value with simulation studies of two concrete applications: segment cleaning and data mining. Free segment cleaning often allows an LFS file system to maintain its ideal write performance when cleaning overheads would otherwise reduce performance 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 effect on its disk performance.