Using Tyan S2882 Dual Opteron motherboard which has integrated SATA
controller. If no PCI controllers (SCSI or SATA) installed, a hard
drive on integrated SATA controller will be detected as /dev/sda. Once
a PCI SCSI or 3Ware SATA controller are installed, the integrated SATA
controller is detected after the PCI controller, so the device
attached to the integrated SATA controller is no longer  detected as
/dev/sda (depends on # of SCSi or SATA drives installed on the PCI
based drive controllers). If the operating system was installed on the
drive connected to the integrated SATA controller, the system won't
boot because the O/S can't be found; get "waiting for device ??? to
appear" messages;

I read somewhere that if you change the order in which modules are
loaded, you can correct this problem.

I need the device containing the O/S to always be detected first, no
matter if drives are added to the system or removed.