Hi Phil,

I recreated the Array and it started.

As you can see, the partition table corresponds to the size of the 
combined devices. Metadata type 0.90 is at the end of each member, so 
the first sector of loop0 will become the first sector of md0. 

Right, /dev/md0 now looks exactly the same as /dev/loop0:

root@ThinkPad /media/Backup/NAS # fdisk -l /dev/md0
Disk /dev/md0: 1638.7 GB, 1638744850432 bytes
255 heads, 63 sectors/track, 199232 cylinders, total 3200673536 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

     Device Boot      Start         End      Blocks   Id  System
/dev/md0p1               1       16064        8032   77  Unknown
/dev/md0p2           16065  3200673535  1600328735+  88  Linux plaintext

quoted

 From what I read in a forum it's possible to mount the XFS partition 
with an offset, in my case that would be 00ae0000 (last line in 
hexdump).

Shouldn't be necessary.  I expect your LV w/ XFS to show up properly.

Nothing happened, so I tried as described in the forum post I mentioned 
(about a pretty much identical NAS and so LVM):

root@ThinkPad /media/Backup/NAS # hexdump -C /dev/md0 | head -n 150 | 
grep XFSB
00ae0000  58 46 53 42 00 00 10 00  00 00 00 00 00 04 00 00  
|XFSB............|

Offset for XFS-Partition is 00ae0000, that's 11403264 in decimal, so I 
tried (read only):

root@ThinkPad /media/Backup/NAS # losetup -r -o 11403264 /dev/loop4 
/dev/md0

and then I got:

root@ThinkPad /media/Backup/NAS # disktype /dev/loop4

--- /dev/loop4

Block device, size 1.490 TiB (1638733447168 bytes)
XFS file system, version 4
   Volume name ""
   UUID 705BF11E-8F69-1CDA-8727-00004868BBE3 (DCE, v1)
   Volume size 1 GiB (1073741824 bytes, 262144 blocks of 4 KiB)

Small progress, but volume size only 1 GiB?
I didn't ran xfs_check or xfs_repair so far because there's probably a 
better way to do it :)

Best regards,
Johannes Moos