From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Raid-0 speed Date: Wed, 25 Aug 2004 09:05:39 +0400 Sender: linux-raid-owner@vger.kernel.org Message-ID: <412C1E23.1070104@wasp.net.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: To: RAID Linux List-Id: linux-raid.ids G'day all, As you would see I have a problem with libata drivers and raid-0. In the process of debugging this I have been doing some speed/throughput tests. On my machine, running 2 instances of dd in 2 terminals dd if=/dev/sdk of=/dev/null & dd if=/dev/sdl of=/dev/null I see over 100MB/s read from VMSTAT. If I pass the dd via pipebench to /dev/null I see between 50-60MB/s read speed from each drive simultaneously. With the raid-0 running, doing a dd if=/dev/md1 of=/dev/null I get about 55MB/s read speed. I can't quite figure out why the md is so slow. Given its using streaming reads with no seeking it should be over 100MB/s. Raid-0 created with mdadm --create --chunk=128 --level=0 --raid-devices=2 /dev/md1 /dev/scsi/host12/bus0/target0/lun0/disc /dev/scsi/host13/bus0/target0/lun0/disc Am I doing something obviously silly? Also, doing a dd from 4 drives maxes out my read speed as per mdstat at 160MB/s (How? PCI is 133MB/s and according to lspci all my controllers are on the same bus). Does vmstat lie? Regards, Brad