From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <xfs-bounces@oss.sgi.com>
Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11])
	by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id
	p66784WM089159 for <xfs@oss.sgi.com>; Wed, 6 Jul 2011 02:08:05 -0500
Date: Wed, 6 Jul 2011 03:07:56 -0400
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: XFS internal error (memory corruption)
Message-ID: <20110706070756.GA25800@infradead.org>
References: <4E12A927.9020102@gmail.com> <20110705130932.GF1026@dastard>
	<4E1313C1.6020309@gmail.com> <20110706040403.GW1026@dastard>
MIME-Version: 1.0
Content-Disposition: inline
In-Reply-To: <20110706040403.GW1026@dastard>
List-Id: XFS Filesystem from SGI <xfs.oss.sgi.com>
List-Unsubscribe: <http://oss.sgi.com/mailman/options/xfs>,
	<mailto:xfs-request@oss.sgi.com?subject=unsubscribe>
List-Archive: <http://oss.sgi.com/pipermail/xfs>
List-Post: <mailto:xfs@oss.sgi.com>
List-Help: <mailto:xfs-request@oss.sgi.com?subject=help>
List-Subscribe: <http://oss.sgi.com/mailman/listinfo/xfs>,
	<mailto:xfs-request@oss.sgi.com?subject=subscribe>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Sender: xfs-bounces@oss.sgi.com
Errors-To: xfs-bounces@oss.sgi.com
To: Dave Chinner <david@fromorbit.com>
Cc: xfs-masters@oss.sgi.com, xfs@oss.sgi.com, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, T?r?k Edwin <edwintorok@gmail.com>

On Wed, Jul 06, 2011 at 02:04:03PM +1000, Dave Chinner wrote:
> > Although is there supposed to be a performance benefit from having
> > a separate log disk with XFS?
> 
> There used to be. Now everyone just uses delayed logging, which is
> far faster and more scalable that even using an external log.

Even with delayed logging external logs are a huge benefit if you
hit the log hard, e.g. for fsync intensive workloads.  E.g. when
using fs_mark in fsync mode it gives speedups over 100% for the
setups I've tested.  You'll see similar speedups for NFS server
loads that are log force heavy as well.

> 
> > IIRC it has a disadvantage that you can't use barriers properly.
> 
> That mostly works now (recent kernels), but you take a hit in
> journal IO waiting synchronously for the data device caches to be
> flushed before writing to the log device.

For metadata-heavy workloads where an external log benefits you most
you generally just want to disable the volatile write cache anyway.

_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs