mdadm -> BTRFS conversion

[Patrick O'Callaghan]

I currently have a pair of external drives configured as ext4 with
RAID1 using mdadm, and mainly used for backup. My / and /home
filesystems are now BTRFS so I'm looking at converting the external
drives to BTRFS with RAID1. My main reason is to take advantage of
BTRFS checksumming as a guard against bitrot, but I'd also like the
flexibility of setting up subvolumes with different properties (the
disks are currently 90% empty).

Any thoughts on this? What would be the simplest conversion strategy if
I go ahead?

poc