FAST 2002 Abstract
Matching Access Patterns to Disk Drive Characteristics
Jiri Schindler, John Linwood Griffin, Christopher R. Lumb, Gregory R. Ganger
Carnegie Mellon University
Track-aligned extents (traxtents) utilize disk-specific
knowledge to match access patterns to the strengths of
modern disks. By allocating and accessing related data
on disk track boundaries, a system can avoid most rotational
latency and track crossing overheads. Avoiding
these overheads can increase disk access efficiency by up
to 50% for mid-sized requests (100Ð500 KB). This paper
describes traxtents, algorithms for detecting track boundaries,
and some uses of traxtents in file systems and video
servers. For large-file workloads, a version of FreeBSD's
FFS implementation that exploits traxtents reduces application
run times by up to 20% compared to the original
version. A video server using traxtent-based requests can
support 56% more concurrent streams at the same startup
latency and buffer space. For LFS, 44% lower overall
write cost for track-sized segments can be achieved.
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