From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Odd (slow) RAID performance Date: Thu, 30 Nov 2006 16:09:06 -0500 Message-ID: <456F4872.2090900@tmr.com> References: <20061130153240.1300912EDE@bluewhale.planbit.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20061130153240.1300912EDE@bluewhale.planbit.co.uk> Sender: linux-raid-owner@vger.kernel.org To: Roger Lucas Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Roger Lucas wrote: >>> What drive configuration are you using (SCSI / ATA / SATA), what chipset >>> >> is >> >>> providing the disk interface and what cpu are you running with? >>> >> 3xSATA, Seagate 320 ST3320620AS, Intel 6600, ICH7 controller using the >> ata-piix driver, with drive cache set to write-back. It's not obvious to >> me why that matters, but if it helps you see the problem I''m glad to >> provide the info. I'm seeing ~50MB/s on the raw drive, and 3x that on >> plain stripes, so I'm assuming that either the RAID-5 code is not >> working well or I haven't set it up optimally. >> > > If it had been ATA, and you had two drives as master+slave on the same > cable, then they would be fast individually but slow as a pair. > > RAID-5 is higher overhead than RAID-0/RAID-1 so if your CPU was slow then > you would see some degradation from that too. > > We have similar hardware here so I'll run some tests here and see what I > get... Much appreciated. Since my last note I tried adding --bitmap=internal to the array. Bot is that a write performance killer. I will have the chart updated in a minute, but write dropped to ~15MB/s with bitmap. Since Fedora can't seem to shut the last array down cleanly, I get a rebuild on every boot :-( So the array for the LVM has bitmap on, as I hate to rebuild 1.5TB regularly. Have to do some compromises on that! Thanks for looking! -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979