[CentOS] Re: raid1 disk format?

Scott Silva ssilva at sgvwater.com
Thu Jun 12 18:08:15 UTC 2008

on 6-12-2008 10:28 AM Les Mikesell spake the following:
> 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.

I know that it seems like an easy way to clone machines, but I think there are 
better and safer ways to clone machines.

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