Computer Science Department
School of Computer Science, Carnegie Mellon University


Towards Higher Disk Head Utilization:
Extracting "Free" Bandwidth From Busy Disk Drives

Christopher Lumb, Jiri Schindler, Gregory R. Ganger,
Erik Riedel*, David F. Nagle

Keywords: Disk scheduling, storage systems

Freeblock scheduling is a new approach to utilizing more of disks' potential media bandwidths. 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 two concrete applications: free segment cleaning and free data mining. Free segment cleaning allows an LFS file system to maintain its ideal write performance when cleaning overheads would otherwise cause up to factor of 3 performance decreases. Free data mining can achieve 45-70 full disk scans per day on an active transaction processing system, with no effect on transaction performance.

31 pages

*Now with Hewlett-Packard Labs, Palo Alto, California,

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