From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: very poor ext3 write performance on big filesystems? Date: Sat, 01 Mar 2008 15:04:29 -0500 Message-ID: <47C9B6CD.3040709@tmr.com> References: <47B980AC.2080806@wpkg.org> <20080218141640.GC12568@mit.edu> <47C54773.4040402@wpkg.org> <20080227200335.GB9331@webber.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Tomasz Chmielewski , Theodore Tso , Andi Kleen , LKML , LKML , linux-raid@vger.kernel.org To: Andreas Dilger Return-path: Received: from mail.tmr.com ([64.65.253.246]:54854 "EHLO gaimboi.tmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756904AbYCAUAd (ORCPT ); Sat, 1 Mar 2008 15:00:33 -0500 In-Reply-To: <20080227200335.GB9331@webber.adilger.int> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Andreas Dilger wrote: > I'm CCing the linux-raid mailing list, since I suspect they will be > interested in this result. > > I would suspect that the "journal guided RAID recovery" mechanism > developed by U.Wisconsin may significantly benefit this workload > because the filesystem journal is already recording all of these > block numbers and the MD bitmap mechanism is pure overhead. > Thanks for sharing these numbers. I think use of a bitmap is one of those things which people have to configure to match their use, certainly using a larger bitmap seems to reduce the delays, using an external bitmap certainly help, especially on an SSD. But on a large array, without a bitmap, performance can be compromised for hours during recovery, so the administrator must decide if normal case performance is more important than worst case performance. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark