Neil Brown wrote:
On Wednesday November 9, andyliebman@xxxxxxxxxxxxx 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
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