Why do I get 'HDIO_GET_IDENTITY failed' message when booting with external usb hard drive?
Solution 1:
This is a warning from hdparm as it can have problems communicating with external usb hard drives, so you can ignore that warning.
Source: 1, 2
Solution 2:
I am getting the same error on a fresh install of Ubuntu 12.04 on an external USB hard disk.
The message is displayed for ~5 sec at boot but ubuntu does boot and run properly after that. I have also noticed some data loss but can't say for certain if its connected to this error.
According to to other help threads on the net this error only appears when Ubuntu is installed on an external USB drive.