I'm currently evaluating Microsoft System Center Data Protection Manager 2010.
When creating a new protection group, I can select to co-locate the client data in the storage pool.
Now, the documentation states:
System Center Data Protection Manager (DPM) allows you to co-locate your protection groups on a volume or tape. Co-locating your protection groups allows you to use your storage more effectively.
Awesome! So, let's enable it.
Now I require almost 10x as much storage space. Why?