If you want to use software raid device in your Gentoo Linux system (init boot, not systemd) with boot partition resided in the raid for better redundancy but using metadata 1.2 version you won’t have autodetection feature on boot and there are some additional steps you may consider!
Linux kernel’s autodetection feature of the software raid is only for superblock (metadata) version 0.90!
If you create a software raid with superblock version 1, 1.1 or 1.2 you want to boot from it you must use:
- Grub 2, lilo won’t load the kernel from such paritions.
- include mdadm in initramfs
- initramfs booted with aditional parameter “domdadm” (in fact, it is not a “native” kernel option, read below)