Are you sure? I can add another storageserver as long as it's not same type as already configured, but not of same type (ex. AdvDisk). In my lab I have one MSDP and one AdvDisk storageserver on my one primary/media server. But get error when trying to add another of any same type. (storageserver xxxxx already exist in NetBackup.).
you can have only one MSPD and adv storage server but multiple "other vendor" storage servers.
As Laurence_Merry said, if the new device have different IP, you must to create a new storage server.
On the other hand, if for any reason you need to create multiple disk pools for the same storage server, this is doable.
To further clarify, the storage server is the device/system that performs the storage operations. You can have only one storage server defined per device/system.
For MSDP and AdvDisk this is the media server, so only one MSDP pool (let's ignore cloud pools for now).
Each DataDomain will be a storage server, they can be configured (I believe) with multiple disk pools.