From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763690AbYB1U0k (ORCPT ); Thu, 28 Feb 2008 15:26:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762302AbYB1U0W (ORCPT ); Thu, 28 Feb 2008 15:26:22 -0500 Received: from mail.tmr.com ([64.65.253.246]:52578 "EHLO gaimboi.tmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761987AbYB1U0U (ORCPT ); Thu, 28 Feb 2008 15:26:20 -0500 Message-ID: <47C719CB.6070704@tmr.com> Date: Thu, 28 Feb 2008 15:30:03 -0500 From: Bill Davidsen User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061105 SeaMonkey/1.0.6 MIME-Version: 1.0 To: Mariella Petrini CC: linux-kernel@vger.kernel.org Subject: Re: Linux and SSD and how to decrease io delay : question, please References: <847418.75727.qm@web35715.mail.mud.yahoo.com> In-Reply-To: <847418.75727.qm@web35715.mail.mud.yahoo.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mariella Petrini wrote: > Hi All, > > I have been running Linux kernel 2.6.23 with Debian on > > a 2 CPUs Dual-Core AMD Opteron(tm) Processor 2218. > I have been using an SSD drive (MTRON) connected to a > raid controller (LSI MegaRAID 8704ELP) to contain > data stored on several databases. > Each database contains 20,000 files and there are 50 > databases total (1,000,000 files distributed across 50 > directories on the filesystem on the ssd). > > The database server uses the databases very "write" > intensively. > An approximate percentage could be 20% reads versus > 80% random writes. > > No matter which filesystem type is used (I have tried > ext3, xfs, jfs, reiserfs) I see every few seconds > snapshots (the could last in the worst case up to 200 > seconds, depending on the filesystem type) > where the iowait on the ssd device goes approximately > over 50% (up to 100%) and > the database server threads go to wait (get > suspended). > > Is there any Linux kernel parameter or any Linux > parameter that could be varied that could help to > decrease the time spent to sync all the data to the > SSD device ? > I may misunderstand the problem, but have you tried tuning the parameters /proc/sys/vm/dirty_* to help this? It sounds as if you may be filling write cache and then flushing. Of course you didn't measure the disk i/o rates along with this, so it's hard to see what's happening. -- Bill Davidsen "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot