If you have Network DLP then you should check with support to see how to properly interface with your storage. For example, is it a Linux NAS, a NetApp, a DFS?
Most storage allows you to limit which persons/groups can access it, such as an AD group membership like "Persons able to access NAS07", then you have your list of persons who CAN access it. Now, determine from WHERE they access it. PC? Laptop? Phone?
You can use the Host DLP in some of these cases (aside from the phone) to limit where data can be copied to by those persons accessing that storage, and combined with NDLP you can better prevent against other network leaks such as if someone emails it out via their phone or something crazy.