From mboxrd@z Thu Jan 1 00:00:00 1970 From: Drew Subject: Re: single threaded parity calculation ? Date: Sat, 16 Apr 2011 06:45:18 -0700 Message-ID: References: <4DA89A18.5010002@mcnair.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <4DA89A18.5010002@mcnair.co.uk> Sender: linux-raid-owner@vger.kernel.org To: simon@mcnair.co.uk Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids > iostat reports 83MB/s for each disk, running up to 830MB/s for all 10 disks, > but the max read speed of the array is approx 256MB/s. This may be a dumb question but what motherboard & disk controllers are you using and how are they setup? That 256MB/s feels to me like you may be bumping up against a bandwidth limitation of your bus. PCI (32bit/33MHz) is limited to 133MB/s max and PCIe(1.0/2.0) is limited to 250/500MB/s per lane. To sustain 830MB/s you need at least a PCIe (1.0) x4 or PCI-X 133 controller card which are both rated for (theoretically) 1GB/s. As an aside, for read speeds on a RAID-5, the parity disk isn't used so theoretical maximum in this case is 9x83MB/s or 747MB/s. ;-) -- Drew "Nothing in life is to be feared. It is only to be understood." --Marie Curie