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CMU-CS-01-119
Computer Science Department
School of Computer Science, Carnegie Mellon University
CMU-CS-01-119
Track-aligned Extents:
Matching Access patterns to Disk Drive Characteristics
Jiri Schindler, John Linwood Griffin,
Christopher R. Lumb, Gregory R. Ganger
April 2001
CMU-CS-01-119.ps
CMU-CS-01-119.pdf
Keywords: Data layout, disk characterization, disk efficiency,
file systems, track-aligned access
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 (100-500 KB). This paper describes traxtents, algorithms for
detecting track boundaries, and use of traxtents in file systems and
video servers. For large file workloads, a modified version
of FreeBSD's FFS implementation reduces application run times by 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.
20 pages
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