btrfsctl no long exists, the utility for scanning btrfs volumes in the latest stable btrfs-progs is 'btrfs' https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices Using the attached patch and the necessary initrd overlay files I was able to get a btrfs RAID 1 on / working. Reproducible: Always
Created attachment 367236 [details, diff] btrfs util name change
https://gitweb.gentoo.org/proj/genkernel.git/commit/?id=d41ebc4d721a8706d0b0f7c5cd1ed8dab42d667c