From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753536AbYJVDHk (ORCPT ); Tue, 21 Oct 2008 23:07:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751226AbYJVDHc (ORCPT ); Tue, 21 Oct 2008 23:07:32 -0400 Received: from turing-police.cc.vt.edu ([128.173.14.107]:44485 "EHLO turing-police.cc.vt.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751126AbYJVDHb (ORCPT ); Tue, 21 Oct 2008 23:07:31 -0400 X-Mailer: exmh version 2.7.2 01/07/2005 with nmh-1.2 To: Jonathan Johnson Cc: linux-kernel@vger.kernel.org Subject: Re: How do I self diagnose slow write to HDD performance issue In-Reply-To: Your message of "Tue, 21 Oct 2008 14:34:01 CDT." <48FDE860.8C56.0056.0@matc.edu> From: Valdis.Kletnieks@vt.edu References: <48FDE860.8C56.0056.0@matc.edu> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1224644845_3562P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Tue, 21 Oct 2008 23:07:25 -0400 Message-ID: <111655.1224644845@turing-police.cc.vt.edu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --==_Exmh_1224644845_3562P Content-Type: text/plain; charset=us-ascii On Tue, 21 Oct 2008 14:34:01 CDT, Jonathan Johnson said: > Before I setup the array I tested the SATA 2 drives connected to the mobo SATA connect and got approx 60mb/s > write and even better read speeds per drive. Remember that streaming read/write speed is usually only a small part of the total disk performance story. Sure, if you don't have to move the heads much, you can go 60 megabytes/sec. However, even the *hottest* drives out there have a hard time sustaining 200 seeks per second. In other words, every time you have to move the heads, it costs you 300Kbytes/sec of throughput (1/200th of that 60M). And bonnie++ probably moves the heads a lot. To *add* insult to injury, if you're running in RAID6 mode, each time you write to the RAID set, it has to do *several* I/Os to do all the parity computations. So you take a 300K hit for each of those I/Os. There's a *reason* why RAID1 is still used - you can (assuming a smart enough controller) launch both the write and the mirroring write at the same time in parallel, taking little or no performance penalty. --==_Exmh_1224644845_3562P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Exmh version 2.5 07/13/2001 iD8DBQFI/pjtcC3lWbTT17ARAgcYAKCdoA4tEiQUCcC6wqM5xfm/qyloawCgxfoM Gf1vU0Ox8uY7msfFAhK4yjo= =4D9Y -----END PGP SIGNATURE----- --==_Exmh_1224644845_3562P--