Hi folks,
I would appreciate it if someone can help me understand some weird
results I'm seeing with trying to do performance testing with an SSD
offloaded ZIL.
I'm attempting to improve my infrastructure's burstable write capacity
(ZFS based WebDav servers), and naturally I'm looking at implementing
SSD based ZIL devices.
I have a test machine with the crummiest hard drive I can find installed
in it, Quantum Fireball ATA-100 4500RPM 128K cache, and an Intel X25-E
32gig SSD drive.
I'm trying to do A-B comparisons and am coming up with some very odd
results:
The first test involves doing IOZone write testing on the fireball
standalone, the SSD standalone, and the fireball with the SSD as a log
device.
My test command is: time iozone -i 0 -a -y 64 -q 1024 -g 32M
Then I check the time it takes to complete this operation in each scenario:
Fireball alone - 2m15s (told you it was crappy)
SSD alone - 0m3s
Fireball + SSD zil - 0m28s
This looks great! Watching 'zpool iostat-v' during this test further
proves that the ZIL device is doing the brunt of the heavy lifting
during this test. If I can get these kind of write results in my prod
environment, I would be one happy camper.
However, ANY other test I can think of to run on this test machine shows
absolutely no performance improvement of the Fireball+SSD Zil over the
Fireball by itself. Watching zpool iostat -v shows no activity on the
ZIL at all whatsoever.
Other tests I've tried to run:
A scripted batch job of 10,000 -
dd if=/dev/urandom of=/fireball/file_$i.dat bs=1k count=1000
A scripted batch job of 10,000 -
cat /sourcedrive/$file > /fireball/$file
A scripted batch job of 10,000 -
cp /sourcedrive/$file /fireball/$file
And a scripted batch job moving 10,000 files onto the fireball using
Apache Webdav mounted on the fireball (similar to my prod environment):
curl -T /sourcedrive/$file http://127.0.0.1/fireball/
So what is IOZone doing differently than any other write operation I can
think of???
Thanks,
Pat S.
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