I'm trying to set up raid1 on my linux machine and all the tutorials explain changing your grub config. Fine, but I like to understand what I'm doing. The man page for grub leaves out the interesting bits when explaining the root command. The command looks like "root /device/ [hdbias]" and device looks something like "hd(0,0)" or "hd(1,0)" but it doesn't explain what these numbers correspond to, and since my drive setup isn't exactly like theirs I question putting them in my grub config without knowing if I'm pointing to the correct drive. What do the device numbers mean?
Grub is a bit weird in it's device naming scheme. The part that says
tells grub where to find the boot partition. This has to be a physical partition, like sda1. In the above example, hd0,0 means the first partition of the first physical drive. Sadly, grub does not follow the normal convention of calling the first partition 'partition 1', but calls it 'partition 0' instead. Nothing to be done about that.
The line that says
tells the kernel where the root partition is. in this case on a logical volume called /dev/Volume00/LogVol00. The kernel understands LVM and more (grub does not) so it is okay to use LVM or dmraid or whatever here. Be sure to use a ramdisk with the necessary modules though.
if you use the interactive grub shell, tab completion will show you the possible choices for the root device if you type root(hdTAB) or root(hd0,TAB).
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