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Re: PATCH: allow installing grub on the MBR if /boot is on mdraid.

Jeremy Katz wrote:
On Wed, 2008-11-26 at 12:06 +0100, Hans de Goede wrote:
This patch removes a special case when /boot (or / without a separate /boot) is on mdraid. For some reason we only allow installing grub to the mdX device then instead of allowing both the mbr of the 1st disk and the device holding /boot.

I've searched through the anaconda history and this special handling of mdraid /boot has been there since before Feb. 2002, it was inherited from before booty was introduced and it does not seem to make sense. Either we cannot have /boot on mdraid at all (in all cases except for raid1) or we can have /boot on dmraid (in case of raid1) and then it does not matter if the bootstrap of grub starts on the mbr or on the first sector of a partition.

The reason we install to the mdX device is so that if your disk dies,
the bootloader install is mirrored[1] to both disks.  So while it is
technically possible to install to the mbr of the first disk, doing so
loses the redundancy of the RAID install.

Well, that is pretty useless, this could be usefull when the first disk (as seen by the BIOS) dies, except that if 99% of the cases that happens the BIOS will still see the disk and thus still try to boot from it and fail.

Software raid1 really only protects against data loss and keeps the system running when a disk dies. It does not guarantee the system will still (re)boot if a disk dies.

Moreover, grub (booty) does not actually install to the mdX device, it will only install to the first partition of the raid set. Atleast that is how I read the booty code. And this is no surprise as grub does not know anything about mdraid.



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