To support the requirement that virtual tape server systems coexist with native tape systems in the same library, the library manager partitions the physical library into logical libraries: one library for each VTS system (a physical library can contain up to two VTS systems) and another that contains all other systems. This must be done because a virtual tape server system presents the image of 3490-type tape device and yet cannot read or write a real 3490 cartridge. By placing a virtual tape server system in its own logical library, host software will not be able to attempt to allocate a virtual tape server device for a real 3490 mount, and likewise, the other way around.

Each logical library will have its own unique library sequence number and will look like a separate physical library to the hosts attached to the system in that partition. The physical assets used by the system are managed by the library manager in the library.