On Wed, 16 Dec 2009, Bill Sprouse wrote:
I think one of the reasons they went to small recordsizes was an issue where
they were getting killed with reads of small messages and having to pull in
128K records each time. The smaller recordsizes seem to have improved that
aspect at least. Thanks for the pointer to the Dovecot notes.
This is likely due to insufficient RAM. Zfs performs very poorly if
it is not able to cache full records in RAM but the (several/many)
accesses are smaller than the record size.
Dovecot is clearly optimized for a different type of file system.
Something which is rarely mentioned is that zfs pools may be less
fragmented on systems with lots of memory. The reason for this is
that writes may be postponed to a time when there is more data to
write (up to 30 seconds), and therefore more data is written
contiguously or with a better layout. Synchronous write requests tend
to defeat this, but perhaps using a SSD as an intent log may help so
that synchronous writes to disk may also be deferred.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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