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FAST 2002 Abstract

Freeblock Scheduling Outside of Disk Firmware

Christopher R. Lumb, Jiri Schindler, and Gregory R. Ganger, Carnegie Mellon University


Freeblock scheduling replaces a disk drive's rotational latency delays with useful background media transfers, potentially allowing background disk I/O to occur with no impact on foreground service times. To do so, a free-block scheduler must be able to very accurately predict the service time components of any given disk request the necessary accuracy was not previously considered achievable outside of disk firmware. This paper describes the design and implementation of a working external freeblock scheduler running either as a user-level application atop Linux or inside the FreeBSD kernel. This freeblock scheduler can give 15% of a disk's potential bandwidth (over 3.1MB/s) to a background disk scanning task with almost no impact (less than 2%) on the foreground request response times. This can increase disk bandwidth utilization by over 6x.
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Last changed: 27 Dec. 2001 ml
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