Comment 28 for bug 595138

It appears to be fixed in 13.04. Apply the patch above.

Aside: You don't actually need to "patch". You can just edit the /lib/hdparm/hdparm-functions file. It's a 7 line change. Find the line that says DISC=$KEY and wrap it in an "if"

https://launchpadlibrarian.net/73763550/hdparm-functions.patch