I named my first Mac “ExMachina”. New laptops are so much fun. ExMachina is a 2TB 15” MBP. It's receiving its first Time Machine backup to a new 3TB Western Digital MyPassport Ultra ***. Started with the instructions on the Western Digital website re: Erasing the drive first, etc. But at some point, reality differed from instructions. Sierra just took over so I went with it. My data point: The first 100GB backed up, encrypted, took 1 hour, 30 minutes. Is this good? *** 2 days later edit: I've used this WD drive forever with my PCs, but it does NOT work well with the MacBook Pro / Time Machine. I should have researched this better before purchasing. People below said it's Sierra or Time Machine, not the drive The backup never finished. Caused a CPU Machine check. Then, the system would never complete booting with it plugged in. It just kept rebooting. Odd that it took over an hour to calculate the time remaining (12 hours).