1) Go to the "System" settings pane in the Administrative website for the device
2) Expand the "Energy Saver" section
3) Uncheck "Hard Disk Sleep"
This will prevent the hard drives within the WD MyBook Live Duo from going to low power sleep mode, and will make the drive more readily accessible.
Note: I have tried this in the past with this particular drive and it did not work. There have been a couple firmware updates since then (it's been a couple years) and now it appears to work properly. Also worth noting that this may decrease the lifetime of your drives within the device.