Here are a few tips to help you pack the backup data onto the least space on your new backup target.
Do store similar data in the same repository
If for capacity, performance, or other reasons you end up with more than one de-duping backup device, you'll get much better de-duplication factors if you keep the backups of servers that host similar data types together. After all, your users receive files as email attachments, edit them, and send them out as attachments so there will be lots of duplicate data across your email and file servers.
Backing up the system drives of your Windows servers to one appliance and your databases to another will get you better data reduction than backing up the automotive division servers to one and the aerospace division to the other.
Dont encrypt or compress before de-duping
All de-duping algorithms work by identifying common blocks of data and storing them only once. Encrypting or compressing data in your backup application or a SAN appliance before the de-duping algorithm sees it hides the commonality.