Same UUID for every member of all array ?

Same UUID for every member of all array ?

[Brice Figureau]

Hi,

While I was trying to understand while an old server (which was happily
running linux 2.6.16 without initrd) was not booting anymore after a
migration to Etch and a new kernel (2.6.20.6 with initrd), I found the
following issue:

$ mdadm --detail --scan
ARRAY /dev/md0 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md8 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md7 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md6 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md5 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md4 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md3 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md2 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873
ARRAY /dev/md1 level=raid1 num-devices=2
UUID=6b8b4567:327b23c6:643c9869:66334873

As you can see, all the UUIDs are the same, and indeed there is no
possibility for mdadm to assemble such arrays as it uses the UUID to
find matching members.

Now, I don't know why all the UUID are equals (my other machines are not
affected).

Is there a possibility to "hot" change the UUID of each array (and
change the corresponding superblocks of each member) so that my next
boot will work ?

I'm not subscribed to the list, so please CC: me on replies.

Thanks,
--
Brice Figureau

Re: Same UUID for every member of all array ?

[Iustin Pop]

On Thu, Apr 12, 2007 at 02:57:57PM +0200, Brice Figureau wrote:
> Now, I don't know why all the UUID are equals (my other machines are not
> affected).
I think at some point either in sarge or in testing between sarge and
etch, there was included a version of mdadm which had this bug (all
arrays had the same uuid). Yeah, it bit me too a little :)

> Is there a possibility to "hot" change the UUID of each array (and
> change the corresponding superblocks of each member) so that my next
> boot will work ?
did you read the manpage for mdadm (the version in etch)? It has a -U
argument to assemble which does what you want.

regards,
iustin

Re: Same UUID for every member of all array ?

[Brice Figureau]

Hi,

Thanks for the answer,

On Fri, 2007-04-13 at 09:32 +0200, Iustin Pop wrote:
> On Thu, Apr 12, 2007 at 02:57:57PM +0200, Brice Figureau wrote:
> > Now, I don't know why all the UUID are equals (my other machines are not
> > affected).
> I think at some point either in sarge or in testing between sarge and
> etch, there was included a version of mdadm which had this bug (all
> arrays had the same uuid). Yeah, it bit me too a little :)

I wasn't aware of the issue - guess I should have noticed that issue
when creating the arrays first.

After searching, the problem appeared because Debian packaged mdadm
version 1.8.1 which wasn't stable. 
Here is one of the debian bug report:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=290363

> > Is there a possibility to "hot" change the UUID of each array (and
> > change the corresponding superblocks of each member) so that my next
> > boot will work ?
> did you read the manpage for mdadm (the version in etch)? It has a -U
> argument to assemble which does what you want.

Yes, I read it (and now twice :-)). 

The problem is that right now the server is up and running (booting with
an old kernel without initrd starts the arrays without any issue, that's
strange), so I can't change the UUID (as it has to be done while
assembling the array).

I first need to reboot with an initrd kernel that fails to assemble the
root array, and issue the mdadm assemble by hand. To do that I must be
physically in front of the console. And this will incur downtime for the
users of this particular server, hence my question about "hot" changing
the UUID...

Anyway, many thanks for your help,
-- 
Brice Figureau <brice+lklm@daysofwonder.com>