From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Re: Raid-0 speed Date: Thu, 26 Aug 2004 13:54:35 +0400 Sender: linux-raid-owner@vger.kernel.org Message-ID: <412DB35B.7090802@wasp.net.au> References: <412C1E23.1070104@wasp.net.au> <87k6vneok0.fsf@enki.rimspace.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87k6vneok0.fsf@enki.rimspace.net> To: Daniel Pittman Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Daniel Pittman wrote: >>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. > > > Your chunk size is way to low to give good streaming reads. The kernel > needs to switch between devices every 128 kilobytes, while is rather > low. > > Try slowly pushing the chunk size to 16384 and see when your performance > gets back up to your expected level. Nope.. Any chunk size > 4096 gives me too big chunk_size: 8388608 > 4194303. And the performance difference between chunk=16 and chunk=4096 is less than 5MB/s --chunk=16 gives me 48.43 MB/s --chunk=4096 gives me 51.52 MB/s Regards, Brad