I just got my WD 3 TB hard drive. I put it in an external dual disk duplicator (max USB3) and partitioned and formatted it GUID with partitions of 2.2 TB and 800 GB. The larger partition was for Time Machine backup for my iMac.
I then transferred the new drive to an older external case (USB2, FW400, FW800 & eSATA). That device would only see the 800 GB partition in Disk Utility, and it would see it as a disk, not as a partition. I tried moving the 3 TB drive to another external case (USB3) and it would show me the 800 GB and the 2.2 TB partitions as disks.
I put the hd back in the original duplicator and used Disk Utility to create one partition of 3 TB. Testing the previous two other external housings they showed the exact results as in the previous paragraph. They were NOT seeing the newly made 3 TB partition, but seeing the two partitions as disks.
I opened my desktop computer, connected the hd. Windows 7 saw the 3 TB drive as a large 3TB partition and a small 200 MB EFI partition. The EFI partition was not removable. I tried using the command line Diskpart to remove all the partitions and change the partition table to MBR. The EFI partition would not budge.
On a MacPro computer the hd was seen as a normally formatted single partition 3 TB drive. On a second try it saw the two partitions as disks. OS X's diskutil showed the partitions as disks as well. For good measure I reformatted the drive again to a single partition 3 TB drive. I took note that Disk Utility did not allow me to change from GUID to MBR.
The net result was after many attempts to remedy the curious EFI partitioning table issue, showing different partitioning schemes dependent on the device that they were in. This is very scary re trusting my data to it. How can I fix or remove the EFI partition and start all over again?