From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Mon, 12 Nov 2007 12:32:06 -0800 (PST) Received: from larry.melbourne.sgi.com (larry.melbourne.sgi.com [134.14.52.130]) by oss.sgi.com (8.12.11.20060308/8.12.10/SuSE Linux 0.7) with SMTP id lACKVqKU028467 for ; Mon, 12 Nov 2007 12:31:56 -0800 Date: Tue, 13 Nov 2007 07:31:47 +1100 From: David Chinner Subject: Re: [[PATCH, RESEND]] less AGs for single disks configs. Message-ID: <20071112203147.GA995458@sgi.com> References: <20071031233516.GB88034736@melbourne.sgi.com> <1194839329-22003-1-git-send-email-xaiki@sgi.com> <1194839329-22003-2-git-send-email-xaiki@sgi.com> <1194839329-22003-3-git-send-email-xaiki@sgi.com> <1194839329-22003-4-git-send-email-xaiki@sgi.com> <1194839329-22003-5-git-send-email-xaiki@sgi.com> <1194839329-22003-6-git-send-email-xaiki@sgi.com> <20071112090147.GD66820511@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Justin Piszcz Cc: xaiki@sgi.com, xfs@oss.sgi.com On Mon, Nov 12, 2007 at 09:57:21AM -0500, Justin Piszcz wrote: > On Mon, 12 Nov 2007, David Chinner wrote: > >A single spindle, regardless of it's size, will have similar > >seek characteristics so scaling the number of AGs with size > >is the wrong thing to do - you don't get better parallelism > >out of a single spindle, just more seeks and lower performance. > >hence keeping the number of AGs fixed up to the point where > >the AG size tops out (i.e. 4TB) seems like a better scaling > >factor to me. i.e. something like: > > > > > > if (!multidisk) { > > if (dblocks >= TERABYTES(4, blocklog)) { > > blocks = XFS_AG_MAX_BLOCKS(blocklog); > > goto done; > > } > > agcount = 4; > > /* work out ag size here */ > > goto done; > > } > > > >I'd also like to see some test results showing the mkfs output > >for the different configurations to confirm it works correctly > >(i.e. that the corner cases work correctly). > > Dave, when this is put into place do you recommend people re-format their > XFS partitions for those with a 750GiB drive -or- with a < 2TB RAID5 > array, No. If you are having performance problems, then changing the way the filesystem is laid out *may* improve performance but if everything is working fine then don't change it. > would one see any increase in speed? On a single disk, yes. On RAID5 - who knows. There are so many other variables to raid5 performance (esp software raid) that such single disk optimisations could degrade performance. On other RAID hardware, it might improve - it really depends on the RAID implementation.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group