From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Mon, 21 Aug 2006 07:23:04 -0700 (PDT) Received: from sccrmhc12.comcast.net (sccrmhc12.comcast.net [63.240.77.82]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id k7LEMoDW027117 for ; Mon, 21 Aug 2006 07:22:50 -0700 Message-ID: <44E9A6B3.8000607@comcast.net> Date: Mon, 21 Aug 2006 08:27:31 -0400 From: Brian Davis MIME-Version: 1.0 Subject: Re: Differences in su/sw values for hw vs. sw RAID 5? References: <082120060155.2003.44E912A400010D0F000007D322058864429C07900E0B079D0D@comcast.net> <44E94F90.1010606@agami.com> In-Reply-To: <44E94F90.1010606@agami.com> 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: Shailendra Tripathi Cc: xfs@oss.sgi.com Maybe I'm missing something, but I'm not sure how the information below maps to setting the values on Hardware RAID. A nice feature of xfs is that it's intelligent enough to figure out the proper values for SW RAID. Thanks! Shailendra Tripathi wrote: > 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]] >> >> >