Metadata Update Performance in File Systems
Gregory R. Ganger, Yale N. Patt
Department of EECS, University of Michigan
ganger@eecs.umich.edu
Abstract
Structural changes, such as file creation and block allocation, have
consistently been identified as file system performance problems in
many user environments. We compare several implementations that
maintain metadata integrity in the event of a system failure but do
not require changes to the on-disk structures. In one set of schemes,
the file system uses asynchronous writes and passes ordering
requirements to the disk scheduler. These scheduler-enforced ordering
schemes outperform the conventional approach (synchronous writes) by
more than 30 percent for metadata update intensive benchmarks, but are
suboptimal mainly due to their inability to safely use delayed writes
when ordering is required. We therefore introduce soft updates, an
implementation that asymptotically approaches memory-based file system
performance (within 5 percent) while providing stronger integrity and
security guarantees than most UNIX file systems. For metadata update
in- tensive benchmarks, this improves performance by more than a
factor of two when compared to the conventional approach.
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