I have about 6 external USB drives that are mostly 1TB or 1.5TB. I have been trying to copy files from old ones to new ones but if I plug in more than two they keep unmounting with the message that the drive was not unmounted properly and may now be damaged. I have two so far that are corrupted. I have tried three different powered USB hubs thinking it was lack of power but it made no difference. This problem occurs on my 26" iMac Running Lion and on my new PowerBookPro running Mavericks.
Can anyone please advise what to do. I am afraid that if I keep pulling plugs in and out to change drives I will end up with damaged USB ports.