There are three ways to stop it from writing to disk... 1) Unplug it from the wall. This is the "maximum energy saving mode." 2) Tune to music stations. Audio only stations are not recorded. 3) Tune to unavailable channels -- either channels that do not exist or unauthorized channels. It obviously cannot record what it doesn't have.
I've never understood why Tivo, Inc. even made "standby". A) Tivos don't draw a huge amount of power to begin with. B) "Standby" doesn't shut off any of the power sucking bits. (like the mpeg encoder, mpeg decoder, hard drive, and/or cpu.) [Granted, DTivos don't have encoders.]