Re: Partition larger than 2 TB?
The standard Linux fdisk utility works only on MBR disks and on some more exotic disk types, but not on GPT disks. Thus, from post #1 it's obvious that you're trying to create MBR partitions, not GPT partitions. To create or modify GPT partitions, you must use gdisk (an fdisk workalike) or a libparted-based tool (parted, GParted, etc.), as others have said.
Since your initial example shows you working on /dev/sdb, it appears that you've got a true hardware RAID controller. With such a controller, you can treat the array as if it were a physical disk of that size, so you don't need to worry about some of the software RAID issues that can cause problems sometimes. If you're booting in BIOS mode, though, you'll need to create a ~1 MiB BIOS Boot Partition, as oldfred has said; and you'll need to ensure that your kernel falls below the 2 TiB mark. The most reliable way to do this is to create a separate /boot partition (which is entirely different from the BIOS Boot Partition) and put the /boot partition before the 2 TiB mark on the disk. If you've got a new motherboard with UEFI support, you should create a ~200-250MB EFI System Partition (ESP) instead of a BIOS Boot Partition. If you're not sure which you've got, you can create both partitions.
You do not need to recompile an Ubuntu kernel to use GPT -- at least, not any recent version of Ubuntu. I've got several 11.04 installations on GPT disks with stock kernels and they're all fine.
If I've suggested a solution to a problem and you're not the original poster, do not try my solution! Problems can seem similar but be different, and a good solution to one problem can make another worse. Post a new thread with your problem details.