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CMU-CS-01-149
Computer Science Department
School of Computer Science, Carnegie Mellon University
CMU-CS-01-149
Freeblock Scheduling Outside of Disk Firmware
Christopher R. Lumb, Jiri Schindler, Gregory R. Ganger
July 2001
CMU-CS-01-149.ps
CMU-CS-01-149.pdf
Keywords: Disk scheduling, storage systems, fisk efficiency, file systems
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 freeblock 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 increases disk bandwidth utilization by over 6x.
18 pages
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