12 TB Disk In freebsd AMD 64 ?

[Dan Naumov]

MBR can only work with 2TB volumes, however, we are no longer limited
to MBR. With GPT, we can have really really big volumes. That being
said, I really don't think you should be using a single 12TB volume
with UFS, even if you have underlying redundancy provided by a
hardware raid device. Have you ever had to fsck a 2TB volume or
bigger? It's not fun. My recommendation would be to use ZFS. Use it to
manage your array and filesystems and use it on top of individual raw
disk devices, if you must use your raid controller, use it in JBOD
mode.

If you want a relatively technical introduction to ZFS and why it's
good for you, read up here:
http://www.slideshare.net/relling/zfs-tutorial-usenix-june-2009

- Sincerely,
Dan Naumov