On Wed, 25 Apr 2007, PaweÅ~B GruszczyÅ~Dski wrote:
I was just reading some informations on the web (for example: http://www.nabble.com/a-comparison-of-ext3,-jfs,-and-xfs-on-hardware-raid-t144738.html).
You were doing your tests with a database scale of 50. As Heikki already pointed out, that's pretty small (around 800MB) and you're mostly stressing parts of the system that may not change much based on filesystem choice. This is even more true when some of your tests are only using a small amount of transactions in a short period of time, which means just about everything could still be sitting in memory at the end of the test with the database disks barely used.
In the example you reference above, a scaling factor of 1000 was used. This makes for a fairly large database of about 16GB. When running in that configuration, as stated he's mostly testing seek performance--you can't hold any significant portion of 16GB in memory, so you're always moving around the disks to find the data needed. It's a completely different type of test than what you did.
If you want to try and replicate the filesystem differences shown on that page, start with the bonnie++ tests and see if you get similar results there. It's hard to predict whether you'll see the same differences given how different your RAID setup is from Jeff Baker's tests.
It's not a quick trip from there to check if an improvement there holds up in database use that's like a real-world load. In addition to addressing the scaling factor issue, you'll need to so some basic PostgreSQL parameter tuning from the defaults, think about the impact of checkpoints on your test, and worry about whether your WAL I/O is being done efficiently before you get to the point where the database I/O is being measured usefully at all via pgbench.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD
