From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <3AEF2F97.E70A8CA7@loria.fr> Date: Tue, 01 May 2001 23:50:15 +0200 From: Dominique LARCHEY-WENDLING MIME-Version: 1.0 Subject: Re: [linux-lvm] LVM & high system load References: <200105011618.KAA01133@lynx.turbolabs.com> Content-Transfer-Encoding: 7bit Sender: linux-lvm-admin@sistina.com Errors-To: linux-lvm-admin@sistina.com Reply-To: linux-lvm@sistina.com List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-lvm@sistina.com Andreas Dilger wrote: > There is one other person that has reported very slow LVM performance. > However, there is no obvious reason why they have performance issues, > and others are unable to reproduce this problem. > > Can you please try the following and report results: > > time dd if=/dev/mmedia/music of=/dev/null bs=512 > time dd if=/dev/mmedia/music of=/dev/null bs=65536 > time dd if=/dev/hda1 of=/dev/null bs=512 > time dd if=/dev/hda1 of=/dev/null bs=65536 Here are the tests I have done ... I use the command line dd if=/dev/sda of=/dev/null bs=1k count=500k to fill up the buffer cache before any timing measure. I point out that /dev/mmedia/music resides on /dev/hda5 time dd if=/dev/mmedia/music of=/dev/null bs=512 count=200000 0m37.113s time dd if=/dev/hda5 of=/dev/null bs=512 count=200000 0m35.437s Ok I am ridiculous ... this has nothing to do with LVM. It has to do with DMA set off by default by linux 2.4. This is the reason of poor IO perf. and CPU eating. (as you might have understood, I usually do not use IDE drives) After DMA is set on, time dd if=/dev/mmedia/music of=/dev/null bs=512 count=200000 0m12.934s time dd if=/dev/hda5 of=/dev/null bs=512 count=200000 0m12.110s Sorry for anoying you with my stupidity ... Perhaps poor perf. for the other person is also DMA related ?-) Thanks anyway DL -- Dominique Larchey LORIA, Nancy, France Tel. (Work) +33 (0) 3 83 59 20 13