Ok. I have been trying to do some research on the gpt partition format vs the mbr partition format. I have a 16 port raid card that currently has 2 2tb arrays and a 1.2tb array using mbr partitions. I would like to be able to combine the 2tb arrays into one big 4tb array. I know that mbr is limited to 2tb size. My question is there a downside to using a gpt partition format? All my pc's are running vista ultimate sp1 or vista business so I'm not worried about compatibility with prior os's.