From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id q69C1TYF222469 for ; Mon, 9 Jul 2012 07:01:29 -0500 Received: from mail-pb0-f53.google.com (mail-pb0-f53.google.com [209.85.160.53]) by cuda.sgi.com with ESMTP id T92VxgLp0gHD9t0Y (version=TLSv1 cipher=RC4-SHA bits=128 verify=NO) for ; Mon, 09 Jul 2012 05:01:28 -0700 (PDT) Received: by pbbrr13 with SMTP id rr13so23859026pbb.26 for ; Mon, 09 Jul 2012 05:01:28 -0700 (PDT) Date: Mon, 9 Jul 2012 20:02:28 +0800 From: kedacomkernel Subject: Re: Re: mkfs.xfs states log stripe unit is too large References: <20120623234445.GZ19223@dastard> <4FE67970.2030008@sandeen.net> <4FE710B7.5010704@hardwarefreak.com> <20120626023059.GC19223@dastard> <20120626080217.GA30767@infradead.org> <20120702061827.GB16671@infradead.org> <20120702164113.109162be@notabene.brown>, <20120702080802.GQ19223@dastard> Mime-Version: 1.0 Message-ID: <201207092002243437160@gmail.com> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-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 , Neil Brown Cc: Christoph Hellwig , linux-raid , Ingo J?rgensmann , xfs On 2012-07-02 16:08 Dave Chinner Wrote: >On Mon, Jul 02, 2012 at 04:41:13PM +1000, NeilBrown wrote: >> On Mon, 2 Jul 2012 02:18:27 -0400 Christoph Hellwig wrote: >> >> > Ping to Neil / the raid list. >> >> Thanks for the reminder. >> >> > [snip] > >That's true, but the characterisitics of spinning disks have not >changed in the past 20 years, nor has the typical file size >distributions in filesystems, nor have the RAID5/6 algorithms. So >it's not really clear to me why you;d woul deven consider changing >the default the downsides of large chunk sizes on RAID5/6 volumes is >well known. This may well explain the apparent increase in "XFS has >hung but it's really just waiting for lots of really slow IO on MD" >cases I've seen over the past couple of years. > At present, cat /sys/block/sdb/queue/max_sectors_kb: is 512k. Maybe because this. >The only time I'd ever consider stripe -widths- of more than 512k or >1MB with RAID5/6 is if I knew my workload is almost exclusively >using large files and sequential access with little metadata load, >and there's relatively few workloads where that is the case. >Typically those workloads measure throughput in GB/s and everyone >uses hardware RAID for them because MD simply doesn't scale to this >sort of usage. > >> If 512K is always suboptimal for XFS then that is unfortunate but I don't > >I think 512k chunk sizes are suboptimal for most users, regardless >of the filesystem or workload.... > >> think it is really possible to choose a default that everyone will be happy >> with. Maybe we just need more documentation and warning emitted by various >> tools. Maybe mkfs.xfs could augment the "stripe unit too large" message with >> some text about choosing a smaller chunk size? > >We work to the mantra that XFS should always choose the defaults >that give the best overall performance and aging characteristics so >users don't need to be a storage expert to get the best the >filesystem can offer. The XFS warning is there to indicate that the >user might be doing something wrong. If that's being emitted with a >default MD configuration, then that indicates that the MD defaults >need to be revised.... > >If you know what a stripe unit or chunk size is, then you know how >to deal with the problem. But for the majority of people, that's way >more knowledge than they are prepared to learn about or should be >forced to learn about. > >Cheers, > >Dave. >-- >Dave Chinner >david@fromorbit.com >-- >To unsubscribe from this list: send the line "unsubscribe linux-raid" in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs