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Abstract - Technical Program - OSDI 99
Virtual Log Based File Systems for a Programmable Disk
Randolph Y. Wang, University of California, Berkeley
Thomas E. Anderson, University of Washington, Seattle
David A. Patterson, University of California, Berkeley
Abstract
In this paper, we study how to minimize the latency of small
synchronous writes to disks. The basic approach is to write to free
sectors that are near the current disk head location by leveraging the
embedded processor core inside the disk. We develop a number of
analytical models to demonstrate the performance potential of this
approach. We then present the design of a virtual log, a log
whose entries are not physically contiguous, and a variation of the
log-structured file system based on this approach. The virtual log
based file systems can efficiently support small synchronous writes
without extra hardware support while retaining the advantages of LFS
including its potential to support transactional semantics. We compare
our approach against traditional update-in-place and logging systems
by modifying the Solaris kernel to serve as a simulation engine. Our
evaluations show that random synchronous updates on an unmodified UFS
execute up to an order of magnitude faster on a virtual log than on a
conventional disk. The virtual log can also significantly improve LFS
in cases where delaying small writes is not an option or on-line
cleaning would degrade performance. If the current trends of disk
technology continue, we expect the performance advantage of this
approach to become even more pronounced in the future.
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Technical Program