From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maurice Hilarius Subject: Awful RAID5 random read performance Date: Sat, 30 May 2009 15:46:32 -0600 Message-ID: <4A21A938.6050907@harddata.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids A friend writes: On a recent machine set up with Raid5. On a AMD Phenom II X4 810, and 4GB ram. 4 Seagate 7200.12 SATA 1TB drives, I'm getting some rather impressive numbers for sequential read (300MB/s+) and write (170MB/s+) but the random read is proving to be absolutely atrocious. iostat says its going at about 0.5MB/s, I've seen plenty of references to people getting numbers in the double digits for random reads on a md raid5 array, and one with slower disks to boot. I tried disabling automatic acoustic management on the drives, but it didn't seem to help at all. I really don't care that much about the noise coming from a file server stuck in a closet ;) Does anyone know why I'm seeing such bad random read times? There's got to be some configuration error on my part, but I just can't seem to find what it might be. I've spent a few hours on google looking for various tweaks but almost nobody even mentions random read/write times. All everyone seems to care about is block sequential access time. I'd be willing to sacrifice a fair portion of my rather excellent sequential times for much better random access. -- Regards, Maurice