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Abstracts - 1997 ANNUAL TECHNICAL CONFERENCE
Embedded Inodes and Explicit Grouping:
Exploiting Disk Bandwidth for Small Files
Gregory R. Ganger and M. Frans Kaashoek
Laboratory for Computer Science,
Massachusetts Institute of Technology,
Cambridge MA 02139 USA
Abstract
Small file performance in most file systems is limited by slowly
improving disk access times, even though current file systems improve
on-disk locality by allocating related data objects in the same general
region. The key insight for why current file systems perform poorly is
that locality is insufficient - exploiting disk bandwidth for small data
objects requires that they be placed adjacently. We describe
C-FSS (Co-locating Fast File System), which introduces two techniques,
embedded inodes and explicit grouping, for exploiting what
disks do well (bulk data movement) to avoid what they do poorly
(reposition to new locations).
With embedded inodes, the inodes for most
files are stored in the directory with the corresponding name, removing
a physical level of indirection without sacrificing the logical level of
indirection. With explicit grouping, the data blocks of multiple small
files named by a given directory are allocated adjacently and moved to
and from the disk as a unit in most cases. Measurement for our C-FSS
implementation show that embedded inodes and explicit grouping have the
potential to increase small file throughput (for both reads and writes)
by a factor of 5-7 compared to the same file system without these
techniques. The improvement comes directly from reducing the number of
disk accesses required by an order of magnitude. Preliminary experience
with software-development applications shows performance improvements
ranging from 30-300 percent.
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