Yes what you've described will work except for having to shrink the
second partition a little for the backup GPT header. mdadm guides have
got you there; should be pretty simple for a RAID-1 that's not totally
full.
As I have indicated, I am deleting everything in the disk as I convert
to GPT with same size MD partition. I have about 32G of free space to
work with as the current MBR partition 1 is empty/unused. So, there
should be no issues with secondary table at the end. The new partitions
will automatically move up a bit and RAID rebuild will take care of
initializing the new partition after I clobber the disk and recreate a
new GPT layout.
Most people seem to opt for having two ESPs that are kept in sync and
thus both/either are selectable from the firmware boot process.
I am not too worried about any redundancy on EFI/boot partitions as a
broken EFI is easy to fix with booting install disk in rescue mode and
reinstalling grup again.
Regards
Ramesh
