From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <3AB59501.FF6ED9F3@dataventures.com> Date: Sun, 18 Mar 2001 22:11:29 -0700 From: Donald Thompson MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [linux-lvm] Apparent performance degradation for each PV with striping Sender: linux-lvm-admin@sistina.com Errors-To: linux-lvm-admin@sistina.com Reply-To: linux-lvm@sistina.com List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-lvm@sistina.com I started playing with iostat tonight and saw a few things I didn't really expect to see. I've got a volume group consisting of 4 82 gig drives. All 4 are IDE drives. Reading directly from the raw device, a PV in this case, with something like dd if=/dev/ide/host0/bus0/target0/lun0/disc of=/dev/null gave me around 5500 blocks read per second. Reading from a unstriped LV on a single PV gives me around 4500 blocks read per second, which I felt was reasonable. When I create a LV striped across all four, my blocks read per second drops to around 1100 per hard drive, giving me a total of about 4400 reads per second for that LV. 2200 reads per second if I striped it across 2 PV's. Timing how long it took to finish a dd for the different types of LV's I made pretty much confirmed what iostat was saying. It always took me 45 seconds, give or take a second, to read a 100 megabyte LV. So it appears striping is useless for me, atleast with this hardware setup. I notice during the dd operation that my system CPU state is 90% or more. So I think I just answered my own question, I'm CPU bound. Moving on, is there any known ways to improve my performance off each PV with this type of hardware setup? I usually create an LV with... lvcreate -i4 -I4 -L somesize vgname -n lvname Should I expect that I won't see the performance drop on individual PV's with striping on SCSI drives? I originally setup this system with no intentions of it being a high performance file server, until a few people I work with decided they wanted to use it for a database machine. So I'm not afraid to spend a couple grand to get some faster disks in it if thats the only thing thats gonna help me. My system: Linux 2.4.2 Libc 2.1.3 Debian Potato LVM 0.9.1_beta6 utilities and patch. ATA 100 IDE interfaces on MB idebus set to 66 in /etc/lilo.conf CPU is Athlon 1000mhz thunderbird 256 megs of RAM -Don