From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Liebman Subject: Re: Still Need Help on mdadm and udev Date: Thu, 10 Nov 2005 20:18:49 -0500 Message-ID: <4373F179.6040301@editshare.com> References: <1200.146.115.27.35.1131563572.squirrel@webmail.editshare.com> <1235.146.115.27.35.1131564483.squirrel@webmail.editshare.com> <17266.60719.545745.800152@cse.unsw.edu.au> Reply-To: AndyLiebman@editshare.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17266.60719.545745.800152@cse.unsw.edu.au> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Wednesday November 9, andyliebman@editshare.com wrote: > >>> Okay, >>> >>> PLEASE somebody who knows answer the following: >>> >>> 1) what is the difference between running >>> >>> mdadm -A -ayes 1/dev/md1--uuid=xxxxx /dev/sd* >>> >>> and >>> >>> mdadm -A -amd 1/dev/md1 --uuid=xxxxx /dev/sd* >>> >>> >>> In other words, how do the "yes" and "md" options behave >>> differently. >>> > > From 'man mdadm' > > -a, --auto{=no,yes,md,mdp,part,p}{NN} > Instruct mdadm to create the device file if needed, possibly allocat- > ing an unused minor number. "md" causes a non-partitionable array to > be used. "mdp", "part" or "p" causes a partitionable array (2.6 and > later) to be used. "yes" requires the named md device to have a from > this. See DEVICE NAMES below. > > Hmmm. there is some text missing there. It should read: > > -a, --auto{=no,yes,md,mdp,part,p}{NN} > Instruct mdadm to create the device file if needed, possibly > allocating an unused minor number. "md" causes a non-partition- > able array to be used. "mdp", "part" or "p" causes a partition- > able array (2.6 and later) to be used. "yes" requires the named > md device to have a 'standard' format, and the type and minor > number will be determined from this. See DEVICE NAMES below. > > (typo in the mdadm.8 source file). > > Does that help? > > >>> 2) If you create an array /dev/md0 with mdadm, is there any reason why >>> you shouldn't start it as /dev/md1? >>> > > No technical reason. This works perfectly. > > > >>> The second option above (-amd 1) would NOT start an array that was created >>> as /dev/md0 (under an older mdadm -- 1.8.? ) whereas the first option >>> (-ayes /dev/md1) had no difficulty. >>> >>> Thank you. >>> Andy Liebman >>> >>> >>> >> Sorry, my bad: >> >> I meant to give as my examples: >> >> mdadm -A -amd 1 --uuid=xxxxx /dev/sd* >> > > This is wrong. It will create a device files called '1' in the > current directory (assuming it works at all). > > >> and >> >> mdadm -A -ayes /dev/md1 --uuid=xxxxx /dev/sd* >> > > Given that /dev/md1 is a 'standard' format name, this will have the > same effect as "-amd /dev/md1". You only get the difference when you > want to use a name like "/dev/md/home" or "/dev/swap", in which case, > "-ayes" isn't allowed as mdadm cannot differentiate between > partitioned and not. > > > NeilBrown > > Thank you Neil. I get it now. I guess it WOULD have been helpful to have that missing text you supplied above!! I really wasn't interested in doing anything I couldn't do two years ago with mdadm -- /dev/mdX was all I wanted or needed. But still, a few concrete examples in "man mdadm" would helpful . For instance, I don't think it's clear that you can create DEVICE NAMES like /dev/md/home. It's a little fuzzy what exactly you are allowed to substitute for {NN}. So, it might be useful to give a few more explicit examples: mdadm -A -ayes /dev/md1 --uuid=xxxxx /dev/sd* OKAY mdadm -A -ayes /dev/md/home --uuid=xxxxx /dev/sd* NO GOOD mdadm -A -amp /dev/md1 --uuid=xxxxx /dev/sd* OKAY mdadm -A -amp /dev/md/home --uuid=xxxxx /dev/sd* OKAY mdadm -A -amp /dev/md/5 -- uuid=xxxxx /dev/sd* IS THIS OKAY? ...etc, for other options. I guess it's also the same for "mdadm -C" (spelling it out always helps tremendously). In fact, I suppose the MOST important examples would be for "mdadm -C" -- because if you can't create an array, you certainly won't be assembling one! It just so happens that in my case I was assembling arrays that had been created on another OS that used devfs and an older version of mdadm. And finally, you might give a phrase after each example indicating why you might want to create a device with such a name. I understand creating a swap partition on a RAID, but I've never heard of naming a RAID device /dev/swap. So, you might give a hint about what the advantage of the latter could be (if there is an advantage). I'm not trying to make work for you. If I could answer these questions, I'd be happy to make this additions to the man page. Thanks again. Couldn't get my work done without mdadm... Andy Liebman