On Wed, 18 Jul 2007, Tang Tse wrote:
Are you using the same part of the disk for both tests?
- Yes on both, is an old scsi controller but supported ( I checked the HLC )
Is the OpenBSD fs using softdep?
- How can i check this?
`mount -v` will report 'softdep' for the filesystem in question if it is
enabled. I believe you need to manually enable it and doing so should
increase general OpenBSD disk performance, not sure for this specific
test.
What is the amount of memory in the machine?
- 2Gb
How many runs is this the average of?
- On linux in the same conditions ( clean install, dd from the same
partition, etc.. ) i get 17MB/s
Is the input_file created immediately before the test?
Yes on both
This, the amount of memory available, and the size of the file probably
causes the biggest difference. IIRC, linux uses almost all available
memory as filesystem cache, but OpenBSD uses 5% by default. In this
case, the 1GB file will have been placed in fs cache when created on
linux, but not on OpenBSD since it wouldn't fit.
In other words, on linux you are testing reading from memory and writing
to disk, but in OpenBSD you are testing reading from disk and writing to
disk.
A couple ways around this would be to either test files > 2GB or to create
the file, umount the partition, mount it, then run dd. If you run IOzone
instead of dd, the results can show you the performance of each system
both when files fit in the memory cache and once it's out. What
performance characteristics are best for your app is for you to decide
(and often a bit beyond anything dd proves).
Is the machine running other processes at the same time?
Yes, I made a new instalation with minimum but i don't disable anything. I
want to test it on daily conditions to see the real performance.
While that's nice and generally safe, you'll also need to be aware of
what's happening in the background that might be time dependant and
different between the two machines. E.g. testing OpenBSD on Saturday
early morning while it's updating the locate database will show different
results versus any other time of day.
Thanks.
Good luck,
-f
http://www.blackant.net/
