Scott Silva wrote:
>
>>>>>> I'm curious as to why 2 complete dd'd copies don't pair at boot.
>>>>>> One comes up running and it does work to mdadm --add the partner
>>>>>> partitions and after the resync they do automatically pair at boot.
>>>>>>
>>>>> Are they dd copies of the different nodes (IE.. dd copy of sda
>>>>> paired with dd copy of sdb)?
>>>>
>>>> No - what was sda was dd'd twice with the dups put in sda and sdb.
>>>>
>>> That is why it didn't work. The superblock knows which drive it was
>>> on, and knows if there are dupes.
>>
>> But I thought the locations were re-detected at boot/assembly time.
>>
>> The other question is whether it is possible to change the uuid while
>> the system is running or if it would have to be done from a CD boot.
>> I've cloned several machines from one initial setup and if copies of
>> the disks ever find their way back into one box I'd prefer not to have
>> the wrong set try to re-sync.
>>
> The locations can re-detect, but I still think it will stop if it
> detects 2 identical superblocks.
> I don't think you can change the UUID of a running array, and I'm not
> sure if you can do it easily on a stopped array. I think the safest
> thing is to use the --add to join the pair. Since they are dd clones,
> the sync should be fairly fast. Just be careful.
Yes, the sync does work fine and once finished the set will always start
itself.
> I know that it seems like an easy way to clone machines, but I think
> there are better and safer ways to clone machines.
You can't beat dd for getting everything exactly the same regardless of
what you changed - or just splitting the mirrors and letting each sync
to new partners but then you have to reinstall grub. I prefer
clonezilla for non-raid configurations but most of the machines I care
about are configured with raid1.
--
Les Mikesell
lesmikesell at gmail.com