backing up a virtual machine to a local USB hard drive

A virtual machine can't natively see USB hard drives. The USB hard drives are attached to the host OS and not visible by the virtual machine. I wondered how to get a virtual machine created in Hyper-V to see a local USB drive and I found this excellent tutorial:

http://blog.ronnypot.nl/?p=721

A summary:

In the host OS, go to disk management and take the USB drive offline (right click on it and choose offline)

Shut down the virtual machine you want the USB drive to attach to.

Open the settings for that virual machine

Go to SCSI controller -> hard drive

Under phsyical hard disk, select the USB drive, which should be visible there

Now you'll be able to see the USB drive in the virtual machine and back up to it if that's what you'd like to do.