Unable To Format NTFS Partition With Allocation Unit Size Of 512B

This is an issue with trying to use the Windows Backup utility with an external hard drive (Seagate GoFlex Desk) with more than 2TB of storage (in this case 3TB). I have looked into this and found that this is a common problem related to the backup utility being unable to deal with drives that have a 4kb allocation unit size. The typical advice is to reformat with an allocation size of 512B, which it will be able to work with.

The problem is that Windows will not let me reformat with that size. The smallest unit it allows is 4kb, which is exactly the problem. If I initiate the format dialog on other NTFS drives I have, 512B shows up as an option. Just not on my external. And yet, this solution appears all over the place and people have claimed it solved their problem. I have even (twice) tried creating a second partition on the external (1.5TB and then 1TB), neither has allowed an allocation unit size less than 4k, even though my 1TB internal drive did allow this.

I am not really interested in third party backup or imaging programs. With my old 500GB external, I used the Windows Backup utility to make a few system images and there have been at least two situations where a bad driver or something has resulted in having to go back to a restore point, but finding no suitable ones available, and thus restoring to the backup image. This has been the simplest way of recovering from these disasters and it has worked every time. For normal file backups, I have a number of cloud storage systems and I can use the software Seagate included with the drive. However, the one and only reason I got a hard drive this large is that it would allow me to make a lot of Windows system images, and that is the one thing I am unable to do. I do not understand why I cannot use the one fix everyone online recommends. I have emailed Seagate tech support about this but they have not responded.