[CentOS] *very* ugly mdadm issue

Thu Sep 4 14:59:30 UTC 2014
Lamar Owen <lowen at pari.edu>

On 09/02/2014 07:36 PM, Joseph L. Casale wrote:
>> Wait just a minute.  How can you use the raw device but still have a GPT
>> on it?  That doesn't seem right, to have a GUID Partition Table but no
>> partitions.
> Have you never deleted all the partitions on a disk under any scheme before?
Of course; but in the context of an MD RAID device with member devices 
as raw disks I would not expect a partition table of any kind, GPT or 
otherwise.  Whether it can be there or not is not my point; it's whether 
it's expected or not.

Now, for C6 the default RAID superblock is version 1.2; but if you were 
to create a version 1.1 superblock it would go on the very first sector 
of the raw device, and would overwrite the partition table.  (The 1.2 
superblock goes 4K in from the first sector; prior to 1.1 the superblock 
went to the last sector of the drive).

Of course, ext4 at least for block group 0 skips the first 1k bytes.....