I have two identical 2.5 Tb WD hard drives in my system. One drive currently shows up as 2.5 tb under disk management in windows 7 64 bit while the other drive only shows as being 280 Gb. The 280 gb is all that shows up regardless of whether it is partitioned or not. I am using GPT and not MBR. I use a hot swap tray. Seems that both drives were showing at 2.5 Tb when I first started using them.