I've recently setup a box with a 3ware RAID controller. After compiling the kernel with genkernel i found out that the root fs could not be mounted because the module for the 3w-xxxx controller was not loaded. In my opinion it should be included when doscsi is specified as a kernel parameter. To fix my problem, i added 3w-xxxx to /usr/share/genkernel/x86/modules_load under MODULES_SCSI. It should be added for x86_64 too, in my opinion. It would be nice to include this so I don't have to remember to add it there should genkernel be updated.
I've added it to CVS
Fixed in 3.4.0_pre1, thanks.