[CentOS] 3TB disk with 6.0.4 not booting

As you know I've been testing centos on an old mac pro.  I have 1 disk left
of 4 that I'm testing on.  I had a 3TB disk and stuck it in and couldn't
get centos to boot off of it.  It would install, but not boot.  I then got
"old" disk 4 installed with it. Any idea why the 3TB disk doesn't work?  I
pulled out an os x 10.6.3 and that would install and boot.  I resized the
disk in osx and reinstalled centos, but centos still won't boot off the 3TB
disk.

Thanks,

-wes