I've been having the same issue for a while, which I posted here
It works well for a while and then I get I/O errors like you have mentioned. Not sure if it's inactivity that's causing this problem, as I set up cron to create a 5 MB file every minute to see if this would still happen, and it did, but I'm sure the hard drive is not failing as it works fine on other devices.
If you google 'raspberry pi usb external input/output errors' you'll get so many people reporting the same problem, but no solution... I don't know if getting a more expensive hub would solve the problem or just be a waste of money.