From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Sun, 20 Aug 2006 23:16:42 -0700 (PDT) Received: from ext.agami.com (64.221.212.177.ptr.us.xo.net [64.221.212.177]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id k7L6GMDW021190 for ; Sun, 20 Aug 2006 23:16:26 -0700 Received: from agami.com ([192.168.168.133]) by ext.agami.com (8.12.5/8.12.5) with ESMTP id k7L6FjwI024137 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO) for ; Sun, 20 Aug 2006 23:15:50 -0700 Received: from mx1.agami.com (mx1.agami.com [10.123.10.30]) by agami.com (8.12.11/8.12.11) with ESMTP id k7L6FeNv021152 for ; Sun, 20 Aug 2006 23:15:40 -0700 Message-ID: <44E94F90.1010606@agami.com> Date: Mon, 21 Aug 2006 11:45:44 +0530 From: Shailendra Tripathi MIME-Version: 1.0 Subject: Re: Differences in su/sw values for hw vs. sw RAID 5? References: <082120060155.2003.44E912A400010D0F000007D322058864429C07900E0B079D0D@comcast.net> In-Reply-To: <082120060155.2003.44E912A400010D0F000007D322058864429C07900E0B079D0D@comcast.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-To: xfs-bounce@oss.sgi.com List-Id: xfs To: bridavis@comcast.net, xfs@oss.sgi.com For RAID-5 device, for any write, the parity as well has to be calculated before writing. In absence of any column of RAID, it is read from disk and then re-written. When you choose writes such as all columns are already there, parity can be directly calculated and written (without incurring any extra read I/O) and that's why, declaring in that form is desirable. Someone correct me if I am wrong. # mdadm --create /dev/md15 --level=5 --raid-devices=3 -c 64 /dev/sd[hvi]1 mdadm: array /dev/md15 started. When forced choice of sw=1,su=128k # cat /proc/mdstat | more ... md15 : active raid5 sdv1[2] sdi1[1] sdh1[0] 78139904 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU] # mkfs.xfs -f -d sw=1,su=128k /dev/md15 mkfs.xfs: Specified data stripe unit 256 is not the same as the volume stripe unit 128 meta-data=/dev/md15 isize=256 agcount=16, agsize=1220928 blks = sectsz=512 data = bsize=4096 blocks=19534848, imaxpct=25 = sunit=32 swidth=32 blks, unwritten=1 naming =version 2 bsize=4096 log =internal log bsize=4096 blocks=9568, version=1 = sectsz=512 sunit=0 blks realtime =none extsz=131072 blocks=0, rtextents=0 Though by default, it detects the former one. # mkfs.xfs -f /dev/md15 meta-data=/dev/md15 isize=256 agcount=16, agsize=1220944 blks = sectsz=512 data = bsize=4096 blocks=19534976, imaxpct=25 = sunit=16 swidth=32 blks, unwritten=1 naming =version 2 bsize=4096 Please note that default created here is: sunit=16, swidth=3 bridavis@comcast.net wrote: > I getting conflicting reports as to how I should generate my sunit/swidth vaules for hardware RAID 5. > > Setup: hardware RAID 5, 3 disks at 300 GBs each, 64k stripe size. > > Originally, following the man page and the mailing list archives, I came up sw=2,su=64k. > > However, I read a reply to an earlier question I sent to the list, and it indicated that the hardward RAID should be treated as a single disk, so I came up with sw=1,su=128k. > > Which one is correct for my setup? > > Thanks! > > [[HTML alternate version deleted]] > >