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/

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