Windows 7 backup to 3TB Seagate external drive got 0x8078002A error

Here is the official answer from Seagate support. Hopefully this sheds some light. One word of caution. There are various online complaints about DiscWizard and my experience with it hasn't been very good either (eg. backup has to be on an entire drive/partition, instead of some folder; the included DriveCleanser doesn't actually do anything).

Thank you for contacting Seagate Support. I am sorry for any inconvenience but Windows Backup does not support 4K sectors. All hard drives now use 4K sectors. You will need to use an older model external hard drive or a different image backup program. Seagate has a program from Acronis called DiscWizard that works on 4K sector hard drives.

Here is a link for the software:

http://www.seagate.com/support/downloads/discwizard/

For additional assistance, feel free to contact us at: http://www.seagate.com/about/contact-us/technical-support/

I just ran into the same problem with a WD drive... so here's a summary for everyone else who googles this page:

The "root cause" is that Windows 7 (and its system tools) does not support a 4K native block size. As a workaround the disk can be formatted with "Advanced Format"/512E to use 512K blocks. KB article 2510009 describes the current support policy and how to check your disk.

After formatting with Windows' Disk Management tool I ended up with a 4K disk layout which did not work for Windows Backup. -- Using the WD Quick Formatter I could reformat the disk to a 512E layout and it works now. Other vendors should provide similar tools.