A specific example of a disk i/o problem (was: FreeBSD vs Ubuntu)

Dieter freebsd at sopwith.solgatos.com
Wed Sep 30 04:24:43 UTC 2009

> > My question is why is FreeBSD's disk i/o performance so bad?
> As I mentioned... this was discussed actively in slashdot. You will  find 
> there many good comments on this.

All I saw in slashdot was a ffs vs ext comment.  I don't believe the problems
I'm seeing are filesystem related.

> > Not just in the benchmarks with debugging on, but in real world usage
> > where it actually matters.
> Are you saying this from actual experience or from reading other people's 
> comments?

Here is a specific demo of one disk i/o problem I'm seeing.  Should be
easy to reproduce?


This was over a year ago, so add 7.1 to the list of versions with the problem.
I believe that the
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 1148109, size: 4096
messages I'm getting are the same problem.  A user process is hogging
the bottleneck (disk buffer cache?) and the swapper/pager is getting starved.

I frequently see problems where disk i/o on one disk starves a process that
needs disk i/o on a different disk on a different controller, which is why
I suspect the disk buffer cache as the bottleneck.

> If it is from actual experience and XYZ version of Linux does a 
> particular job better then I don't see why you should not consider using 
> what works best.

I was stuck running Linux on one machine for awhile and it scrambled my data.
No thank you.  Data integrity is essential.  Thankfully I have been penguin
free for awhile now.

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