Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 30 Apr 2002 08:26:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 30 Apr 2002 08:26:52 -0400 Received: from buzz.etsit.upm.es ([138.100.17.60]:38149 "HELO buzz.etsit.upm.es") by vger.kernel.org with SMTP id ; Tue, 30 Apr 2002 08:26:51 -0400 Date: Tue, 30 Apr 2002 14:23:17 +0200 (CEST) From: Jaime Medrano To: Subject: raid1 performance Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org I have several raid arrays (level 0 and 1) in my machine and I have noticed that raid1 is much more slower than I expected. The arrays are made from two equal hds (/dev/hde, /dev/hdg). And some numbers about the read performances are: /dev/hde: 29 Mb/s /dev/hdg: 29 Mb/s /dev/md0: 27 Mb/s (raid1) /dev/md1: 56 Mb/s (raid0) /dev/md2: 27 Mb/s (raid1) These numbers comes from hdparm -tT. I have noticed a very poor performance when reading sequentially a large file from raid1 (I suppose this is what hdparm does). I have taken a look at the read balancing code at raid1.c and I have found that when a sequential read happens no balancing is done, and so all the reading is done from only one of the mirrors while the others are iddle.? I have tried to modify the balancing algorithm in order to balance also sequential access, but I have got almost the same numbers. I have thought that the reason may be that some layer bellow is making reads of greater size than the chunks in which I balance, and so the same work is being done twice; but I don't know the way to find this. Does anybody know how this works? Regards, Jaime Medrano - 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/