For Debian we use some code which handles all disks from a software raid md array. Have a look at
https://github.com/faiproject/fai/blob/master/examples/simple/scripts/GRUB_PC/10-setup BTW, with grub 2 a device.map is not needed any more. Currently I'm testing the new code for GRUB-PC/10-setup on Debian. -- regards Thomas