I had an external, WD Passport, 1TB disk drive formatted as an HFS+ drive which I was using on my Mac Os X 10.7 machine. After a while, I decided to move the external drive to my Windows 7 machine. Seeing as the drive was already formatted on my Mac machine, Windows 7 was unable to fully initialize the drive because of the EFI Partition.
After running a quick search on Google, I found a quick how-to by David Vielmetter on Deleting An EFI Partition In Windows 7 via the Window’s “diskpart“ tool.
In an effort to preserve the contents of his post, in case the link ever changes, I have copied the list of steps from the original post – minus the images.
[step 1] With the external drive connected. Open the Windows command prompt with elevated privileges (Run as Administrator).
[step 2] When in the command prompt enter the command diskpart to enter the disk partition utility.
[step 3] Type list disk to see a list of available disks. If you are unclear which disk is actually the external drive you can view the correct disk number in the Windows Disk Manager (Start -> Search Box -> diskmgmt.msc). Once the correct disk has been identified type select disk # where # is the disk containing the EFI partition.
[step 4] Type select partition # where # is the partition you wish to delete.
[step 5] Type delete partition override
[step 6] After deleting the partition I noticed that I had to disconnect and reconnect the external drive for the changes to take effect. The disconnect/reconnect can be accomplished, within the disk partition utility, by typing the following commands offline disk; then online disk
Please note that while the steps listed above solved my problem they can lead to the lost of data if not used correctly. So I advise that use it with caution and, if possible, test it on a test environment.