Unable to extend partition with gdisk on XenServer 6.5
Solution 1:
Let gdisk verify the disk for problems (key v).
In my case it identified:
The secondary header's self-pointer indicates that it doesn't reside at the end of the disk. If you've added a disk to a RAID array, use the 'e' option on the experts' menu to adjust the secondary header's and partition table's locations.
I used x e.
Then m(ain menu) p showed the "last usable sector" as expected.