From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Raid-10 mount at startup always has problem Date: Mon, 29 Oct 2007 09:22:51 -0400 Message-ID: <4725DEAB.4050507@tmr.com> References: <46E4A39C.8040509@amfes.com> <46E4A5F0.9090407@sauce.co.nz> <46E4A7C3.1040902@amfes.com> <471F5542.3020504@amfes.com> <471FA485.6010705@tmr.com> <47202D17.3040000@amfes.com> <1193294406.10336.76.camel@firewall.xsintricity.com> <20071026091513.GB32550@percy.comedia.it> <1193426793.10336.302.camel@firewall.xsintricity.com> <4725278E.1050306@tmr.com> <20071029074139.GA15475@percy.comedia.it> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20071029074139.GA15475@percy.comedia.it> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Luca Berra wrote: > On Sun, Oct 28, 2007 at 08:21:34PM -0400, Bill Davidsen wrote: >>> Because you didn't stripe align the partition, your bad. >>> >> Align to /what/ stripe? Hardware (CHS is fiction), software (of the RAID > the real stripe (track) size of the storage, you must read the manual > and/or bug technical support for that info. That's my point, there *is* no "real stripe (track) size of the storage" because modern drives use zone bit recording, and sectors per track depends on track, and changes within a partition. See http://www.dewassoc.com/kbase/hard_drives/hard_disk_sector_structures.htm http://www.storagereview.com/guide2000/ref/hdd/op/mediaTracks.html >> you're about to create), or ??? I don't notice my FC6 or FC7 install >> programs using any special partition location to start, I have only >> run (tried to run) FC8-test3 for the live CD, so I can't say what it >> might do. CentOS4 didn't do anything obvious, either, so unless I >> really misunderstand your position at redhat, that would be your >> bad. ;-) >> >> If you mean start a partition on a pseudo-CHS boundary, fdisk seems >> to use what it thinks are cylinders for that. > Yes, fdisk will create partition at sector 63 (due to CHS being > braindead, > other than fictional: 63 sectors-per-track) > most arrays use 64 or 128 spt, and array cache are aligned accordingly. > So 63 is almost always the wrong choice. As the above links show, there's no right choice. > > for the default choice you must consider what spt your array uses, iirc > (this is from memory, so double check these figures) > IBM 64 spt (i think) > EMC DMX 64 > EMC CX 128??? > HDS (and HP XP) except OPEN-V 96 > HDS (and HP XP) OPEN-V 128 > HP EVA 4/6/8 with XCS 5.x state that no alignment is needed even if i > never found a technical explanation about that. > previous HP EVA versions did (maybe 64). > you might then want to consider how data is laid out on the storage, but > i believe the storage cache is enough to deal with that issue. > > Please note that "0" is always well aligned. > > Note to people who is now wondering WTH i am talking about. > > consider a storage with 64 spt, an io size of 4k and partition starting > at sector 63. > first io request will require two ios from the storage (1 for sector 63, > and one for sectors 64 to 70) > the next 7 io (71-78,79-86,97-94,95-102,103-110,111-118,119-126) will be > on the same track > the 8th will again require to be split, and so on. > this causes the storage to do 1 unnecessary io every 8. YMMV. No one makes drives with fixed spt any more. Your assumptions are a decade out of date. -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979