I have a 1TB G-DRIVE ev (Gen2) which when it is connected works well. What my problem is that to get it connected and actually connected is problematical.
I have to connect the drive a number of times before it is recognised. Not only at the SATA end of the cable but the USB end too. I have tried a number of cables and get the same thing. If it is connected then a slight nudge disconnects it.
The end result is that I tend not to use it especially if I am backing up a large number of large image files.
Is it the SATA connector - USB (of all shapes and sizes ) seem to fit properly as does Thunderbolt. I may just dump this drive and get hold of a Thunderbolt drive