Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751087AbVIRFXH (ORCPT ); Sun, 18 Sep 2005 01:23:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751108AbVIRFXH (ORCPT ); Sun, 18 Sep 2005 01:23:07 -0400 Received: from willy.net1.nerim.net ([62.212.114.60]:13060 "EHLO willy.net1.nerim.net") by vger.kernel.org with ESMTP id S1751087AbVIRFXG (ORCPT ); Sun, 18 Sep 2005 01:23:06 -0400 Date: Sun, 18 Sep 2005 07:23:01 +0200 From: Willy Tarreau To: Al Boldi Cc: linux-kernel@vger.kernel.org Subject: Re: Eradic disk access during reads Message-ID: <20050918052301.GA20422@alpha.home.local> References: <200509170717.03439.a1426z@gawab.com> <200509171323.53054.a1426z@gawab.com> <20050917184643.GA1313@alpha.home.local> <200509180716.46978.a1426z@gawab.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200509180716.46978.a1426z@gawab.com> User-Agent: Mutt/1.5.10i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1586 Lines: 38 On Sun, Sep 18, 2005 at 07:16:46AM +0300, Al Boldi wrote: > Willy Tarreau wrote: > > On Sat, Sep 17, 2005 at 01:32:53PM +0300, Al Boldi wrote: > > > Willy Tarreau wrote: > > > > On Sat, Sep 17, 2005 at 07:26:11AM +0300, Al Boldi wrote: > > > > > Monitoring disk access using gkrellm, I noticed that a command like > > > > > > > > > > cat /dev/hda > /dev/null > > > > > > > > > > shows eradic disk reads ranging from 0 to 80MB/s on an otherwise > > > > > idle system. > > New synonym: eradic=erratic :) I've noticed from the first mail too :-) > > Denis' tool seems clearly more suited to analyse your problem. > > The problem seems to be a multi-access collision in the queue, which forces a > ~50% reduction of thruput, which recovers with another multi-access > collision. Maybe?! do you have anything else connected to the same controller ? I've encountered a problem a long time ago with SATA drives (it was around 2.4.25, with the beginning of SATA support), where I could not use RAID on my drives because simultaneous accesses to the drives was not possible. I then realized that every time I accessed a drive during a read from or a write to another one would stall. I don't remember if CDROM access caused the same trouble. This was with a SATA-patched ata-piix driver, but fortunately this is fixed by now. Regards, Willy - 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/