When Perc3/DC and Perc2/DC are present on a system, RH installs on Perc2/DC. If the Perc2/DC was added with some logical volumes after installing on Perc3/DC, RH tries to boot of the Perc2/DC and the system hangs with the following message "VFS: Cannot open root device 08:06 Kernel panic: VFS: Unable to mount root fs on 08:06". The megaraid (v1.09) always insmod to Perc2/DC first. Slot assignment and cards BIOS Enabling/Disabling doesn't have any effect.
This isn't really an installer issue, but a kernel issue, and fairly generic at that. The question is, in what order should a device driver detect cards that it supports? If you have disks on SCSI controllers such that you violate this order, your root and /boot file systems wind up in the wrong place, and you can't boot. There needs to be a generic way to indicate to the kernel and various device drivers which controller the BIOS thinks is your boot device, and make sure that the right driver is loaded first, and that the right controller is detected first by that driver. Volume labels help a lot, but don't handle the cases of root, /boot, and swap properly, /boot necessary for lilo.
I2O controllers actually let you ask them if they were the boot device (the controller firmware obviously knows this). We put the boot device first then scan the others in PCI order.
Resolved in RH7.1