Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 6 Sep 2002 11:28:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 6 Sep 2002 11:28:20 -0400 Received: from 2-210.ctame701-1.telepar.net.br ([200.193.160.210]:48056 "EHLO 2-210.ctame701-1.telepar.net.br") by vger.kernel.org with ESMTP id ; Fri, 6 Sep 2002 11:28:18 -0400 Date: Fri, 6 Sep 2002 12:32:33 -0300 (BRT) From: Rik van Riel X-X-Sender: riel@imladris.surriel.com To: "Peter T. Breuer" cc: Anton Altaparmakov , Daniel Phillips , Alexander Viro , Xavier Bestel , , Linux Kernel Mailing List Subject: Re: (fwd) Re: [RFC] mount flag "direct" In-Reply-To: <200209061353.g86Drcv06621@oboe.it.uc3m.es> Message-ID: X-spambait: aardvark@kernelnewbies.org X-spammeplease: aardvark@nl.linux.org MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1713 Lines: 48 On Fri, 6 Sep 2002, Peter T. Breuer wrote: > > Chances are your 4-node system would have lower aggregate > > throughput than a single node system. > > IF, and I say IF, it turned out to look that way, we would look for > finer locking instead of abandoning the idea, because the raw arithmetic > at the top of this post is so powerful. Finer grained locking would mean doing IO in smaller chunks and caching less data, which would further decrease the transfer time vs. seek time ratio. If you want an efficient clustered filesystem, I think you should use a filesystem that's designed for clustering. Adding an inefficient kludge on top of ext2 just isn't going to cut it because of your inability to cache metadata and the extremely high cost of disk seeks. The bottleneck isn't bandwidth, it's the latency of a disk seek. A modern hard disk can transfer maybe 60 MB per second when doing linear streaming, but finding one particular place on the disk still takes 10 ms. So in order to get 50% bandwidth efficiency from your disk, you'll need to do IO in chunks of 600 kB. Not caching metadata and having to read directory, inode, indirect block and double indirect block for each piece of data you read is guaranteed to cut your performance by a factor of 10, or more. regards, Rik -- Bravely reimplemented by the knights who say "NIH". http://www.surriel.com/ http://distro.conectiva.com/ Spamtraps of the month: september@surriel.com trac@trac.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/