From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Freemyer Subject: Re: Adding more drives/saturating the bandwidth Date: Wed, 1 Apr 2009 12:15:23 -0400 Message-ID: <87f94c370904010915xd1f5e82sca9e92c9a68884cc@mail.gmail.com> References: <771992.67269.qm@web51307.mail.re2.yahoo.com> <87skks9xg5.fsf@frosties.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <87skks9xg5.fsf@frosties.localdomain> Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: Jon@ehardcastle.com, linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, Apr 1, 2009 at 11:59 AM, Goswin von Brederlow wrote: > Jon Hardcastle writes: > >> --- On Tue, 31/3/09, Goswin von Brederlow wrote: >>> Just see if you can get a decent bandwidth from each disk: >>> >>> for i in /dev/sd?; do dd if=3D$i of=3D/dev/null bs=3D1M >>> count=3D10240 & done >>> iostat -k 10 >>> >>> >>> Halving the bus speed gives you a reasonable low >>> expectation of how >>> much data you should be able to pull of the disks. If your >>> disks can't >>> even fill half the bus bandwidth you certainly can cope >>> with more >>> disks or something is seriously wrong. >>> >>> MfG >>> =A0 =A0 =A0 =A0 Goswin > > Perfectly save. Just don't do it the other way around: > > !!!WARNING WRITE TEST!!! > > for i in /dev/sd?; do dd if=3D/dev/zero of=3D$i bs=3D1M count=3D10240= & done > iostat -k 10 Be advised: on some suse kernels /dev/zero is known to have a performance bug that would keep it from saturating a PCI-express bus. I think it was the kernel they had about a year ago (10.3 release). Greg --=20 Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer =46irst 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.p= df The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html