From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Tue, 15 Jan 2008 13:34:13 -0800 (PST) Received: from larry.melbourne.sgi.com (larry.melbourne.sgi.com [134.14.52.130]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with SMTP id m0FLY1x1002663 for ; Tue, 15 Jan 2008 13:34:05 -0800 Date: Wed, 16 Jan 2008 08:34:10 +1100 From: David Chinner Subject: Re: Proper swidth and sunit for RAID 5 (does it matter)? Message-ID: <20080115213410.GM155407@sgi.com> References: 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: xfs@oss.sgi.com On Tue, Jan 15, 2008 at 12:29:14PM -0500, Justin Piszcz wrote: > Dave, > > What is the proper sunit and swidth for a 64, 256, and 1024 kilobyte chunk > size with a 10-disk raid 5? > > Also, in the majority of benchmarks it does not seem to matter whether the > FS is stripe-aligned or not (with SW raid)- does it mainly/only affect HW > raid? Affects both. If you are doing large I/O, both SW and HW raid will avoid RMW cycles if you can do full stripe writes and that means they go faster. The faster the RAID array, the bigger the difference it will make. If your tests are with small I/O or with a config that can't do I/O large enough for full stripe writes, then you won't see any difference as you're not avoiding RMW cycles. > Current settings (10 disks): > > # xfs_info /dev/md3 > meta-data=/dev/md3 isize=256 agcount=4, agsize=82417536 Why 4 ags? The low number of AGs is an optimisation for single disks, not multi-disk arrays that have much more parallelism and seek capacity available. > blks > = sectsz=4096 attr=2 > data = bsize=4096 blocks=329670144, imaxpct=25 > = sunit=0 swidth=0 blks, unwritten=1 And you don't even have su/sw set here, so XFS won't be doing any alignment optimisation at all. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group