From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: confusion about partitionable md arrays Date: Sat, 30 Dec 2006 17:08:53 -0500 Message-ID: <4596E375.4070900@tmr.com> References: <1167161228.3918.41.camel@localhost.localdomain> <4594897A.4080903@tmr.com> <1167381105.12758.57.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1167381105.12758.57.camel@localhost.localdomain> Sender: linux-raid-owner@vger.kernel.org To: Michael Schmitt Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Michael Schmitt wrote: > Hi Bill, > > this `thing=C2=B4 works in another computer and as I moved it to anot= her one, > I could not get it working. So the problem is... somewhere in between= :) > As I had other non md-related problems in this computer (power supply > insufficient, system could not boot from hda anymore when sata disks > were connected to the pci-controller so I needed to unplug the sata > cables until grub has loaded, BIOS upgrade did not help), I moved the > array back in the original one, and it worked without a change. > > But I noticed there a different behavior "Generating udev events for = MD > arrays" showed up during boot, listing the partitions md0_d0p1 to > md0_d0p4 and of course /dev/md0_d0pN showed up. Then I cogitated abou= t > all that a bit and came to some possible conclusions. Maybe the namei= ng > scheme for the arrays need to reflect somehow if it is a partibionabl= e > array or not, if there are partitions and if udev needs to add the > appropriate devices... or not. Then I remembered some of the strange > things which happend when I did set up the array in the first place. = I > tried to name the array "md0" but /dev/md_0" was generated too. /dev/= md0 > was somehow "dead" and my array was accessible as /dev/md0_d0. A bit > later as I tried to build an array with IDE discs in the "troublesome= " > computer, I noticed similar effects. I tried to name the array > simple /dev/array1 but /dev/md127_d0 (iirc) was generated > too. /dev/array1 was dead and the raid was accessible at /dev/md127_d= 0. > So, whats all that? Even if I had read somehwere the name of the devi= ce > can be anything, it may be that that's not really true. > > So the question remains the same, the confusion is persistent as the > superblocks in my arrays :) Any input is appreciated. > > I already did read some mails in this list but did not get the point = and > no real explanation to my question. I will read on, maybe I get > enlightenment. > =20 I just reread the man page, and there is a paragraph on partitionable=20 arrays following the "-a" option. Having warned you that I'm not=20 experienced in this, I wonder if there is some interaction between=20 device names created by "-amdp" and rules for udev, and how much of thi= s=20 partition info is carried in the superblock. There's a lot of discussio= n=20 of names in that paragraph. I also wonder if using the "-amdp" vs. just "-ap" will work differently= =2E=20 Hopefully Neil will have words of wisdom if we continue to thrash=20 without a good understanding. > greetings > Michael > > Am Donnerstag, den 28.12.2006, 22:20 -0500 schrieb Bill Davidsen: > =20 >> Michael Schmitt wrote: >> =20 >>> Hi list, >>> >>> since recent releases obviously it is possible to build an array an= d >>> partition that instead of building an array out of partitions. This= was >>> somehow confusing but it worked in the first place. Now I moved the >>> array from one machine to another and... now it gets somehow strang= e. I >>> have nothing in /dev/md/ but /dev/md0. If I do fdisk -l it lists th= e >>> partitions /dev/md0p1 to /dev/md0p4, set to type 83 but there are n= o >>> devices under /dev/ or in /proc/partitions for them. I've read the >>> archives and googled around but there was no real solution just >>> different meanings on how it should be and how such things come. I'= d >>> really appreciate a definite answer how that should work with >>> partitionable arrays and in best cases, what my problem may be here= :) >>> >>> At the end of this mail are the mdstat and mdadm outputs for refere= nce >>> >>> =20 >>> =20 >> I'm not sure you have a problem, if this whole thing works correctly= =2E=20 >> However, there has been discussion about the implications of using w= hole=20 >> drives instead of partitions to build your array. Having avoided tha= t=20 >> particular path I'm not going to rehash something I marginally=20 >> understand, but some reading of post in the last few months may shed= =20 >> understanding. >> >> =20 --=20 bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979 - To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html