Arch Linux

Currently RAID support for mkinitcpio is split into two hooks:
* raid
-> This provides RAID support for normal RAID devices like md0. It is included in the mkinitcpio package.
* raid-partitions
-> This provides RAID support for partitionable RAID devices like md_d0. It is included in the mdadm package.

There's a third necessity for the initial ramdisk to boot from a RAID array: mdassemble. It is included in the klibc-extras package.

What I'm proposing is to get rid of both raid & raid-partitions, and replace them with an mdadm hook, that is included in the mdadm package. Attached you will find the mdadm hook & install file.

Advantages over the old method:
* Only one hook for both normal & partitionable RAID arrays;
* No more kernel command line additions for the RAID arrays;
* RAID sets that are degraded can still be booted:
-> With the current setup if you remove a disk, but that disk is still specified on the kernel commandline, the hook will try to assemble the RAID array with all the disks specified. However, since a disk is missing it will fail and you'll be thrown in the emergency shell;
* Should be compatible with the old method, so the old hooks can remain included while systems are migrated to the new mdadm hook (although I don't recommend this - this is a rolling release distro afterall!);
* Device locations don't matter anymore: while the kernel command line requires you to specify devices, mdadm.static is capable of scanning all the devices (see DEVICE or PARTITIONS in mdadm.conf) and figure out which are part of which RAID array.
* Removes ugly code (raid-partitions, yuk!);
* Having mdadm.static in the initcpio means you have the full complement of RAID commands at your disposal in the emergency shell.

Disadvantages:
Nothing I can think of. One could argue that you need a properly configured mdadm.conf, but with the old hooks you'd need a properly configured kernel command line.