* Re: Still Need Help on mdadm and udev
2005-11-10 6:48 ` Neil Brown
@ 2005-11-10 19:29 ` Bill Davidsen
2005-11-10 21:20 ` dean gaudet
2005-11-11 1:18 ` Andy Liebman
1 sibling, 1 reply; 6+ messages in thread
From: Bill Davidsen @ 2005-11-10 19:29 UTC (permalink / raw)
To: Neil Brown; +Cc: andyliebman, linux-raid
On Thu, 10 Nov 2005, Neil Brown wrote:
> 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).
Oh good, I though I was going senile... I haven't had a good use for a
partitionable device, although I can think of some unusual applications
for this, such as creating two RAID-6 partitionable arrarys on separate
controllers, then combining a partition from each as RAID-1 for even more
reliability, and doubg RAID-0 over another two to spread head motion for a
very active application.
Yes, I know there are other ways to do that, it was an example...
--
bill davidsen <davidsen@tmr.com>
CTO TMR Associates, Inc
Doing interesting things with little computers since 1979
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: Still Need Help on mdadm and udev
2005-11-10 6:48 ` Neil Brown
2005-11-10 19:29 ` Bill Davidsen
@ 2005-11-11 1:18 ` Andy Liebman
1 sibling, 0 replies; 6+ messages in thread
From: Andy Liebman @ 2005-11-11 1:18 UTC (permalink / raw)
To: Neil Brown, linux-raid
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
^ permalink raw reply [flat|nested] 6+ messages in thread