From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eli Stair Subject: Re: RAID10: near, far, offset -- which one? Date: Thu, 05 Oct 2006 10:57:13 -0700 Message-ID: <45254779.70506@ilm.com> References: <20061005152321.GA32017@piper.madduck.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20061005152321.GA32017@piper.madduck.net> Sender: linux-raid-owner@vger.kernel.org To: linux-raid mailing list List-Id: linux-raid.ids Taken for what it is, here's some recent experience I'm seeing (not a precise explanation as you're asking for, which I'd like to know also). Layout : near=2, far=1 Chunk Size : 512K gtmp01,16G,,,125798,22,86157,17,,,337603,34,765.3,2,16,240,1,+++++,+++,237,1,241,1,+++++,+++,239,1 gtmp01,16G,,,129137,21,87074,17,,,336256,34,751.7,1,16,239,1,+++++,+++,238,1,240,1,+++++,+++,238,1 gtmp01,16G,,,125458,22,86293,17,,,338146,34,755.8,1,16,240,1,+++++,+++,237,1,240,1,+++++,+++,237,1 Layout : near=1, offset=2 Chunk Size : 512K gtmp02,16G,,,141278,25,98789,20,,,297263,29,767.5,2,16,240,1,+++++,+++,238,1,240,1,+++++,+++,238,1 gtmp02,16G,,,143068,25,98469,20,,,316138,31,793.6,1,16,239,1,+++++,+++,237,1,239,1,+++++,+++,238,0 gtmp02,16G,,,143236,24,99234,20,,,313824,32,782.1,1,16,240,1,+++++,+++,237,1,240,1,+++++,+++,238,1 Here, testing with bonnie++, 14-drive RAID10 dual-multipath FC, 10K 146G drives. RAID5 nets the same approximate read performance (sometimes higher), with single-thread writes limited to 100MB/sec, and concurrent-thread R/W access in the pits (obvious for RAID5). mdadm 2.5.3 linux 2.6.18 xfs (mkfs.xfs -d su=512k,sw=3 -l logdev=/dev/sda1 -f /dev/md0) Cheers, /eli martin f krafft wrote: > I am trying to compare the three RADI10 layouts with each other. > Assuming a simple 4 drive setup with 2 copies of each block, > I understand that a "near" layout makes RAID10 resemble RAID1+0 > (although it's not 1+0). > > I also understand that the "far" layout trades some read performance > for some write performance, so it's best for read-intensive > operations, like read-only file servers. > > I don't really understand the "offset" layout. Am I right in > asserting that like "near" it keeps stripes together and thus > requires less seeking, but stores the blocks at different offsets > wrt the disks? > > If A,B,C are data blocks, a,b their parts, and 1,2 denote their > copies, the following would be a classic RAID1+0 where 1,2 and 3,4 > are RAID0 pairs combined into a RAID1: > > hdd1 Aa1 Ba1 Ca1 > hdd2 Ab1 Bb1 Cb1 > hdd3 Aa2 Ba2 Ca2 > hdd4 Ab2 Bb2 Cb2 > > How would this look with the three different layouts? I think "near" > is pretty much the same as above, but I can't figure out "far" and > "offset" from the md(4) manpage. > > Also, what are their respective advantages and disadvantages? > > Thanks, >