I bought one of these a few weeks ago. I have been having problems with it attached to a two port PCI-E to USB 3.0 Expansion Card. The card has previously worked with all my other drives. I have found it difficult finding someone at Seagate with knowledge of this particular drive to talk about the issues. The suggestion is to run their software which I calculated would take more than two days and I suspect would come out OK. For a while I got it working by having in on at startup with a USB stick inserted in it's port. Now that doesn't work and it knocks out the other USB3 port on the card. It was very cheap per Tb but I wouldn't buy again.
Note, issues with large drives can have many causes, like your OS, USB controller limits, etc.
It looks like you're new here. If you want to get involved, click one of these buttons!