Grub2 with multiple Debians

[Hendrik Boom <hendrik@topoi.pooq.com>]

It has been my practice when upgrading between Debian releases to make 
bootable copies of the OS partitions on my hard drive so that if things 
go badly wrong I still have a bootable system.  And occasionally, things 
have gone badly wrong, so this was a life-saver.

This wirked fine with LILO and GRUB 1, where I was in control of 
configuratino files and could explicitly specifiy which root partitions 
went with which boot partitions/

But when installing grub2 to an MBR. all this is automated.  It looks 
around on the available disks and figures out shoch partition goes with 
which.

Of course, after I've made my copy (with slight changes to /etc/fstab) I 
have two nearly identical sets of partitions, so it may be tricky to tell 
them apart.  Is grub2 clever enough to figure it all out anyway?  And 
what data does it use to this end? (so I can make sure it's right!)

-- hendrik