From mboxrd@z Thu Jan 1 00:00:00 1970 From: Max Waterman Subject: Re: md faster than h/w? Date: Mon, 16 Jan 2006 12:37:40 +0800 Message-ID: <43CB2314.5000203@fastmail.co.uk> References: <20060114212341.GB20464@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: <20060114212341.GB20464@lug.udel.edu> Sender: linux-raid-owner@vger.kernel.org To: Ross Vandegrift Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Ross Vandegrift wrote: > On Sat, Jan 14, 2006 at 01:40:53AM -0500, Mark Hahn wrote: >>> Initially, we were getting 'hdparm -t' numbers around 80MB/s, but this >>> was when we were testing /dev/sdb1 - the (only) partition on the device. >>> When we started testing /dev/sdb, it increased significantly to around >>> 180MB/s. I'm not sure what to conclude from this. >> there are some funny interactions between partitions, filesystems >> and low-level parameters like readahead. > > Hmmm, I'm not convinced, though it could be that the disks in my > workstation are not fast enough. > > I used hdparm and your iorate program to compare the performance on my > fastest disk (7200rpm, ATA100). The difference between partition vs. > disk is definitely within the margin of error: 2-3MB/sec when I'm > averaging around 50MB/sec. > > I'd be suspicious of much more difference between the two... In which case, I'm suspicious - using 'hdparm -t' on h/w RAID0 (4 disks) : /dev/sdb: Timing buffered disk reads: 536 MB in 3.00 seconds = 178.57 MB/sec /dev/sdb1: Timing buffered disk reads: 100 MB in 3.01 seconds = 33.19 MB/sec That's a big difference in my book. However, with bonnie++, using filesystems created on the above devices, I get similar numbers : /dev/sdb: --Sequential Input-- -Per Chr- --Block-- K/sec %CP K/sec %CP 38586 76 126818 15 /dev/sdb1: --Sequential Input- -Per Chr- --Block-- K/sec %CP K/sec %CP 38185 76 127569 15 After running that, I reran hdparm, and it reported ~40MB for *both* /dev/sdb and /dev/sdb1. Then I unmount /dev/sdb and it's back up to 155MB/s !?!?! It's not making any sense to me :( Strange. I guess I should just ignore 'hdparm -t'? Max.