Date: Tue, 29 Sep 2009 19:26:14 PDT From: Dieter <freebsd@sopwith.solgatos.com> To: freebsd-performance@freebsd.org Subject: A specific example of a disk i/o problem (was: FreeBSD vs Ubuntu) Message-ID: <200909300226.CAA29195@sopwith.solgatos.com> In-Reply-To: Your message of "Tue, 29 Sep 2009 12:42:13 EDT." <cone.1254242533.271161.79872.1000@zoraida.natserv.net>
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> > 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? http://lists.freebsd.org/pipermail/freebsd-performance/2008-July/003533.html 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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