On Mon, 15 Jun 2009, Bob Friesenhahn wrote:
On Mon, 15 Jun 2009, Rich Teer wrote:
You actually have that backwards. :-) In most cases, compression is very
desirable. Performance studies have shown that today's CPUs can compress
data faster than it takes for the uncompressed data to be read or written.
Do you have a reference for such an analysis based on ZFS? I would be
interested in linear read/write performance rather than random access
synchronous access.
Perhaps you are going to make me test this for myself.
Ok, I tested this for myself on a Solaris 10 system with 4 3GHz AMD64
cores and see that we were both right. I did an iozone run with
compression and do see a performance improvement. I don't know what
the data iozone produces looks like, but it clearly must be quite
compressable. Testing was done with a 64GB file:
KB reclen write rewrite read reread
uncompressed: 67108864 128 359965 354854 550869 554271
lzjb: 67108864 128 851336 924881 1289059 1362625
Unfortunately, during the benchmark run with lzjb the system desktop
was essentially unusable with misbehaving mouse and keyboard as well
as reported 55% CPU consumption. Without the compression the system
is fully usable with very little CPU consumed.
With a slower disk subsystem the CPU overhead would surely be less
since writing is still throttled by the disk.
It would be better to test with real data rather than iozone.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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