It's a WD 4TB external HDD and it arrived with two roughly equal partitions. One partition is working fine but the other is unallocated and the right-click drop down menu has no options. How am I supposed to format it? Does this mean there's an error on the disk? Never seen this one before.
I took all the files off the disk and tried again to delete the partitions and format the whole disk as one partition but it made no difference. Disk Manager still didn't offer me any of the options I needed.
I succeeded using Diskpart, so I guess all is well.
You would have had to convert the disk from MBR to GPT to use the additional 2GB. That is what Diskpart would have done for you if you got one 4GB partition.