This process was collected by trial and error (mostly error) since most of the documents I found on the 'net were incomplete.
The cookbook/walkthrough on how to grow an Array on EBS at AWS...
# walkthrough by John Jones (jjones at cirrhus9 dot com)
umount /dev/md0
mdadm --stop /dev/md0
REM out the last line in /etc/fstab
# /dev/md0 /mnt/data-files xfs defaults 0 0
REM out the last line of /etc/mdadm/mdadm.conf
# ARRAY /dev/md0 level=raid0 num-devices=2 UUID=31a281bd:50deafca:edf6a245:a7933c25
Stop the instance.
Create new snapshot from existing volumes.
detach "current" sd[xx] volumes.
Create new volume from snapshots at higher capacity.
Attach to same /dev/sdX mount points while the instance is stopped.
Start the instance.
Assign EIP.
Login to the instance.
mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/sdb /dev/sdc
mdadm --examine --scan --config=/etc/mdadm/mdadm.conf >> /etc/mdadm/mdadm.conf
mkdir -v /mnt/data-files
Remove comment in /etc/fstab
/dev/md0 /mnt/data-files xfs defaults 0 0
# check the mount for errors:
xfs_check /dev/md0
# mount it
mount /dev/md0
/dev/md0 40G 49M 40G 1% /mnt/data-files
# Verify new capacity...
mdadm --detail /dev/md0 | grep "Array Size"
Array Size : 83885952 (80.00 GiB 85.90 GB)
# grow the new volumes
xfs_growfs -d /dev/md0
df -h | tail -1
/dev/md0 80G 49M 80G 1% /mnt/data-files
# reboot
reboot
# verify larger capacity
df -h | tail -1
/dev/md0 80G 49M 80G 1% /mnt/data-files
# Verify contents came across
ls -1 /mnt/data-files/
# Done.
Cleanup/delete "old" volumes.
Enjoy!