Bob Friesenhahn wrote:
On Mon, 15 Jun 2009, Thommy M. wrote:
In most cases compression is not desireable. It consumes CPU and
results in uneven system performance.
IIRC there was a blog about I/O performance with ZFS stating that it was
faster with compression ON as it didn't have to wait for so much data
from the disks and that the CPU was fast at unpacking data. But sure, it
uses more CPU (and probably memory).
I'll believe this when I see it. :-)
With really slow disks and a fast CPU it is possible that reading data
the first time is faster. However, Solaris is really good at caching
data so any often-accessed data is highly likely to be cached and
therefore read just one time.
One thing I'm cuious about...
When reading compressed data, is it cached before or after it is
uncompressed?
If before, then while you've save re-reading it from the disk, there is
still (redundant) overhead for uncompressing it over and over.
If the uncompressed data is cached, then I agree it sounds like a total
win for read-mostly filesystems.
-Kyle
The main point of using compression for the root pool would be so
that the OS can fit on an abnormally small device such as a FLASH
disk. I would use it for a read-mostly device or an archive (backup)
device.
On desktop systems the influence of compression on desktop response is
quite noticeable when writing, even with very fast CPUs and multiple
cores.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us,
http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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