From mboxrd@z Thu Jan 1 00:00:00 1970 From: Max Waterman Subject: Re: md faster than h/w? Date: Sat, 14 Jan 2006 09:22:16 +0800 Message-ID: <43C85248.6020405@fastmail.co.uk> References: <20060113144640.GA10566@lug.udel.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20060113144640.GA10566@lug.udel.edu> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Ross Vandegrift wrote: > On Fri, Jan 13, 2006 at 03:06:54PM +0800, Max Waterman wrote: >> One further strangeness is that our best results have been while using a >> uni-processor kernel - 2.6.8. We would prefer it if our best results >> were with the most recent kernel we have, which is 2.6.15, but no. > > Sounds like this is probably a bug. If you have some time to play > around with it, I'd try kernels in between and find out exactly where > the regression happened. The bug will probably be cleaned up quickly > and performance will be back where it should be. > >> So, any advice on how to obtain best performance (mainly web and mail >> server stuff)? >> Is 180MB/s-200MB/s a reasonable number for this h/w? >> What numbers do other people see on their raid0 h/w? >> Any other advice/comments? > > My employer usues the 1850 more than the 2850, though we do have a few > in production. My feeling is that 180-200MB/sec is really excellent > throughput. > > We're comparing apples to oranges, but it'll at least give you an > idea. The Dell 1850s are sortof our highest class of machine that we > commonly deploy. We have a Supermicro chassis that's exactly like > the 1850 but SATA instead of SCSI. On the low-end, we have various P4 > Prescott chassis. > > Just yesterday I was testing disk performance on a low-end box. SATA > on a 3Ware controller, RAID1. I was quite pleased to be getting > 70-80MB/sec. > > So my feeling is that your numbers are fairly close to where they > should be. Faster procs, SCSI, and a better RAID card. However, I'd > also try RAID1 if you're mostly interested in read speed. Remember > that RAID1 lets you balance reads across disks, whereas RAID0 will > require each disk in the array to retrieve the data. > OK, this sounds good. I still wonder where all the theoretical numbers went though. The scsi channel should be able to handle 320MB/s, and we should have enough disks to push that (each disk is 147-320MB/s and we have 4 of them) - theoretically. Why does the bandwidth seem to plateau with two disks - adding more into the raid0 doesn't seem to improve performance at all? Why do I get better numbers using the file for the while device (is there a better name for it), rather than for a partition (ie /dev/sdb is faster than /dev/sdb1 - by a lot)? Can you explain why raid1 would be faster than raid0? I don't see why that would be... Things I have to try from your email so far are : 1) raid1 - s/w and h/w (we don't care much about capacity, so it's ok) 2) raid0 - h/w, with bonnie++ using no partition table 3) kernels in between 2.6.8 and 2.6.15 Max.