From mboxrd@z Thu Jan 1 00:00:00 1970 From: lsorense@csclub.uwaterloo.ca (Lennart Sorensen) Subject: Re: limits on raid Date: Mon, 18 Jun 2007 14:03:27 -0400 Message-ID: <20070618180327.GP10008@csclub.uwaterloo.ca> References: <18034.479.256870.600360@notabene.brown> <18034.3676.477575.490448@notabene.brown> <20070616020320.GB2002@animx.eu.org> <18035.23867.576212.859440@notabene.brown> <4676BEC2.7090809@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: david@lang.hm Cc: Brendan Conoboy , Neil Brown , Wakko Warner , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org List-Id: linux-raid.ids On Mon, Jun 18, 2007 at 10:28:38AM -0700, david@lang.hm wrote: > I plan to test the different configurations. > > however, if I was saturating the bus with the reconstruct how can I fire > off a dd if=/dev/zero of=/mnt/test and get ~45M/sec whild only slowing the > reconstruct to ~4M/sec? > > I'm putting 10x as much data through the bus at that point, it would seem > to proove that it's not the bus that's saturated. dd 45MB/s from the raid sounds reasonable. If you have 45 drives, doing a resync of raid5 or radi6 should probably involve reading all the disks, and writing new parity data to one drive. So if you are writing 5MB/s, then you are reading 44*5MB/s from the other drives, which is 220MB/s. If your resync drops to 4MB/s when doing dd, then you have 44*4MB/s which is 176MB/s or 44MB/s less read capacity, which surprisingly seems to match the dd speed you are getting. Seems like you are indeed very much saturating a bus somewhere. The numbers certainly agree with that theory. What kind of setup is the drives connected to? -- Len Sorensen