On Mar 16, 2007, at 1:22 PM, Jim Rees wrote:
The only reason to fsync would be to enforce a particular ordering
on the
data written to disk.
For POSIX write semantics, yes?
But there is no question afs is way too aggressive at
syncing.
The main reason behind Rob's fsync patch is because we're using ZFS
on our AFS servers, all 8 of them.
ZFS's current behavior (in the future this will be dynamically
alterable) when dealing with a fsync is that it will flush all
pending IOs in the ZFS intent log (aka ZIL, a write cache) to disk,
and this holds up subsequent write IOs until this is completed.
Because we still run our per-user mail store out of ZFS, fsyncs are
quite expensive because of the sheer amount of data (incoming mail)
being written.
/dale
--
Dale Ghent
UNIX and Storage Systems Specialist
UMBC - Office of Information Technology
ENG 201 - 410-443-1705
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