I use a 1tb My Passport Essential as my Time Machine Backup. I upgraded to from a 2009 iMac to a new 2012 iMac. I did one final backup of about 600gb on the old machine and disconnected the drive and connected it to the new machine. During setup and migration the drive would transfer for about 2 hours then disconnect itself. I wiped the machine, reinstalled OS X and started again. The same thing happened. This time the drive stopped being recognized and need to be reinitialized. I used disk utility and the drive checked out, but I had to do a fresh time machine backup. 10 hours later, I started again. Same disconnection error after about 2 hours. I then did a fresh backup to a LaCie Rugged firewire drive that I had. When the WD failed again, I tried with the Lacie via a Thuderbolt adapter. This time it worked.
Can anyone explain why this is happening? Should I not be using a My Passport as a time machine backup drive? Tech Supprt had no answers.