I would agree with Devin but to flesh out the question of how to setup the volumes I would suggest the following:

1. That you implement a new rollover volume that you assign as your new primary volume. Set the rollover to automatically rollover every year. That way you can take the yearly rollovers and make them removable and archive them away without needing to do any more workflows in the future. You'll also likely want to change your default volume on the root folder of your repository so new entries all start dropping into this new volume.

2. To deal with your existing volume you'll likely need to create a couple removable volumes and use workflow to perform a search for all the data from those date ranges and For Each Entry use Migrate Entry to move it to the archive volume you created.

Between those two items you should be able to chop up your big existing volume and transition to a new volume scheme that will automatically roll over yearly so you can just move those physical volumes to offline storage whenever you want.