Darren J Moffat wrote:
Kyle McDonald wrote:
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?
The decompressed (and decrypted) data is what is cached in memory.
Currently the L2ARC stores decompressed (but encrypted) data on the
cache devices.
So the cache saves not only the time to access the disk but also the CPU
time to decompress. Given this, I think it could be a big win.
-Kyle
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