From mboxrd@z Thu Jan 1 00:00:00 1970 From: david@lang.hm Subject: Re: limits on raid Date: Mon, 18 Jun 2007 11:16:32 -0700 (PDT) Message-ID: 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> <4676C9FF.7060607@redhat.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: <4676C9FF.7060607@redhat.com> Sender: linux-raid-owner@vger.kernel.org To: Brendan Conoboy Cc: Neil Brown , Wakko Warner , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org List-Id: linux-raid.ids On Mon, 18 Jun 2007, Brendan Conoboy wrote: > 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. > > I am unconvinced. If you take ~1MB/s for each active drive, add in SCSI > overhead, 45M/sec seems reasonable. Have you look at a running iostat while > all this is going on? Try it out- add up the kb/s from each drive and see > how close you are to your maximum theoretical IO. I didn't try iostat, I did look at vmstat, and there the numbers look even worse, the bo column is ~500 for the resync by itself, but with the DD it's ~50,000. when I get access to the box again I'll try iostat to get more details > Also, how's your CPU utilization? ~30% of one cpu for the raid 6 thread, ~5% of one cpu for the resync thread David Lang