From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thiemo Nagel Subject: Re: Raid over 48 disks Date: Tue, 18 Dec 2007 22:13:26 +0100 Message-ID: <476837F6.7050404@ph.tum.de> References: <00EF99B2-3BCC-4D75-BC75-8F256B0A2476@gmail.com> <476820B0.9010200@ph.tum.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Justin Piszcz Cc: Norman Elton , linux-raid@vger.kernel.org List-Id: linux-raid.ids >> Performance of the raw device is fair: >> # dd if=/dev/md2 of=/dev/zero bs=128k count=64k >> 8589934592 bytes (8.6 GB) copied, 15.6071 seconds, 550 MB/s >> >> Somewhat less through ext3 (created with -E stride=64): >> # dd if=largetestfile of=/dev/zero bs=128k count=64k >> 8589934592 bytes (8.6 GB) copied, 26.4103 seconds, 325 MB/s > > Quite slow? > > 10 disks (raptors) raid 5 on regular sata controllers: > > # dd if=/dev/md3 of=/dev/zero bs=128k count=64k > 8589934592 bytes (8.6 GB) copied, 10.718 seconds, 801 MB/s > > # dd if=bigfile of=/dev/zero bs=128k count=64k > 3640379392 bytes (3.6 GB) copied, 6.58454 seconds, 553 MB/s Interesting. Any ideas what could be the reason? How much do you get from a single drive? -- The Samsung HD501LJ that I'm using gives ~84MB/s when reading from the beginning of the disk. With RAID 5 I'm getting slightly better results (though I really wonder why, since naively I would expect identical read performance) but that does only account for a small part of the difference: 16k read 64k write chunk size RAID 5 RAID 6 RAID 5 RAID 6 128k 492 497 268 270 256k 615 530 288 270 512k 625 607 230 174 1024k 650 620 170 75 Kind regards, Thiemo