Which rdisk value in boot.ini maps to which disk?
According to Microsoft article Q102873: BOOT.INI and ARC Path Naming Conventions and Usage, the order of rdisk() is:
... the ordinal for the disk on the adapter and is usually a number between 0 and 3.
So it seems it would be the usual order (starting with 0): primary master, primary slave, secondary master, secondary slave. (I have no idea how it works with SATA though.)