To have partitions larger than 2 TeraBytes, you need to create a GPT disk, as opposed to an MBR one. This, however, is
not possible during the installation of CentOS, so you might need to handle it either before the installation (e.g:
with booting a Live CD that supports GPT and creating the partition table before the installation) or after the
installation, with the use of gdisk.
Using gdisk is actually very easy, although you should keep in mind that there is no guarrantee that your data will
be safe.
For this example, installation of CentOS 6.2 was done on a system with one 3 TB disk. During the installation, the following partitions were created:
/dev/sda1 0.5 GB /boot
/dev/sda2 13.0 GB LVM PV (4GB swap, 9GB /root)
This left almost all of the 3 TB on the disk available.
After the installation is done, download gdisk for CentOS 6 from OpenSUSE Build Service. You can also find more
versions of gdisk at rodsbooks.com. Example download:
wget http://download.opensuse.org/repositories/home:/srs5694/CentOS_CentOS-6/x86_64/gdisk-0.8.8-133.1.x86_64.rpm
After the download completes, install with:
yum install gdisk-0.8.8-133.1.x86_64.rpm
You can now very simply convert the MBR partition table to GPT with:
gdisk /dev/sda
The new GPT will be available on the next reboot. You can then create
a partition bigger than 2 TB in the unallocated space, either with
gdisk or with parted, then create a filesystem inside it with mkfs,
and finally mount it and start using it!