HSM dry run or message age script?

["David N. Blank-Edelman" <dnb@ccs.neu.edu>]

Hi-
  We are at a point where we are considering turning on HSM on our poor server to take some space pressure of it until we upgrade to a larger storage setup. I've poked around in the docs a bit and haven't found an indication that there might be a dry-run mode that could tell us just how much data will be sloughed off to secondary storage when it runs for real. Am I just missing it?

If not, does anyone have a script that can take a value you would use for zimbraHsmAge and offer up an approximation of just much data would be moved?

Thanks!
        -- dNb