On Tue, 24 Nov 2009, Paul Kraus wrote:
On Tue, Nov 24, 2009 at 11:03 AM, Richard Elling
<richard.ell...@gmail.com> wrote:
Try disabling prefetch.
Just tried it... no change in random read (still 17-18 MB/sec for a
single thread), but sequential read performance dropped from about 200
MB/sec. to 100 MB/sec. (as expected). Test case is a 3 GB file
accessed in 256 KB records. ARC is set to a max of 1 GB for testing.
arcstat.pl shows that the vast majority (>95%) of reads are missing
the cache.
You will often see the best random access performance if you access
the data using the same record size that zfs uses. For example, if
you request data in 256KB records, but zfs is using 128KB records,
then zfs needs to access, reconstruct, and concatenate two 128K zfs
records before it can return any data to the user. This increases the
access latency and decreases opportunity to take advantage of
concurrency.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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