I created a /dev/md1 raid0 across two drives, added ext4 filesystem, and it's mountable and working fine.
I created a /dev/md2 raid0 across two drives, added ext4 filesystem, and it's also mountable and working fine.
When I try to make a /dev/md0 raid1 using devices /dev/md1 and /dev/md2 it changes the filesystem to linux raid member, and cannot be mounted.
If I add ext4 to the raid1, will it overwrite the underlying raid0 data, or will it apply only to the raid1? I don't understand how the filesystem interacts with mdadm builds.