Design and Implementation of a Freeblock Subsystem

Carnegie Mellon University Parallel Data Lab Technical Report CMU-PDL-03-107, December, 2003.

Eno Thereska, Jiri Schindler, Christopher R. Lumb, John Bucy, Brandon Salmon, Gregory R. Ganger

Electrical and Computer Engineering
Carnegie Mellon University
Pittsburgh, PA 15213


Freeblock scheduling allows background applications to access the disk without affecting primary system activities. This paper describes a complete freeblock subsystem, implemented in FreeBSD. It details new space- and time-efficient algorithms that make freeblock scheduling useful in practice. It also describes algorithm extensions for using idle time, dealing with multi-zone disks, reducing fragmentation, and avoiding starvation of the inner- and outer-most tracks. The result is an infrastructure that efficiently provides steady disk access rates to background applications, across a range of foreground usage patterns.

KEYWORDS: scheduling, disks, asynchronous, interfaces

FULL PAPER: pdf / postscript




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