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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
Abstract
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
Ñ 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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