Re: Moved drives between machines... now, MIA.

[Neil Brown <neilb@suse.de>]

On Tue, 2 Feb 2010 08:35:23 -0800 (PST)
Jon Hardcastle <jd_hardcastle@yahoo.com> wrote:

> --- On Tue, 2/2/10, Ken D'Ambrosio <ken@jots.org> wrote:
> 
> > From: Ken D'Ambrosio <ken@jots.org>
> > Subject: Re: Moved drives between machines... now, MIA.
> > To: "Ryan Wagoner" <rswagoner@gmail.com>
> > Cc: linux-raid@vger.kernel.org
> > Date: Tuesday, 2 February, 2010, 15:36
> > > You did make a new mdadm.conf
> > with the correct devices for each array
> > > right? If not try running and seeing if your arrays
> > come up. If they do
> > > then copy /tmp/mdadm.conf to /etc/mdadm/mdadm.conf
> > >
> > > mdadm --examine --scan --config=partitions >
> > /tmp/mdadm.conf mdadm
> > > --assemble --scan --config=/tmp/mdadm.conf
> > 
> > Hmmm.  I was hoping what I'd been doing had been
> > "wrong" somehow, but what
> > you've got is pretty much what I did.  And here's the
> > output (which
> > confuses the living Hell out of me):
> > 
> > ARRAY /dev/md0 level=raid1 num-devices=2
> > UUID=f2de81aa:ccd40fc9:01dc0b99:e8df86c1
> > ARRAY /dev/md1 level=raid1 num-devices=2
> > UUID=837925b3:f9f0e1b1:02f450c9:474613c9
> > ARRAY /dev/md1 level=raid1 num-devices=2
> > UUID=b6af942c:119cd1fc:02f450c9:474613c9
> > 
> > (Note how the second half of the last two UUIDs is the
> > same, and the last
> > two UUIDs are both for /dev/md1.)
> > 
> > Guess it's time to go to the tapes, huh?
> > 
> > Thanks,
> > 
> > -Ken
> > 
> > 
> 
> So basically all you have done is remove the drives from 1 machine and insert in another? I would really hope that, that would not trash data... I have never tried it mind. i did recently change my drive order though just unplugged and re-plugged in a completely new order.
> 

No, that in itself would not cause a problem.
If you have two machines each with /dev/md1, and you move the devices from
one to the other, that other will appear to have two different  /dev/md1
which would be confusing.  mdadm tries to be careful and will only assemble
one of them, or will assemble them both with different names.

The commonality in the tail of the uuid of the two /dev/md1 array is simply
because they were created with the same HOMEHOST.

You can assemble the arrays manually with something like

 mdadm -As /dev/md1 --uuid=.......
 mdadm -As /dev/md1a --uuid=...there-other-one....

Then look at the contents.

NeilBrown

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