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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.
Just like you had to partition and format your raid 0, you have to partition and format your raid 1. Whatever is currently on the raid 0 volumes will be destroyed as is the case when creating any RAID. – Appleoddity – 2019-01-02T15:40:57.940