For logical tape libraries, please look at this excerpt from SG24-5946-06:
" Multiple logical libraries are an effective way for the library to
simultaneously back up and
restore data from heterogeneous applications. For example, the library can
be partitioned so
that it processes:

   - Commands from Application 1 (about Department X) in Logical Library A
   - Commands from Application 2 (about Department Y) in Logical Library B
   - Commands from Application 3 (about Department Z) in Logical Library C

In this configuration, the storage slots and drives in each logical library
are dedicated to that
library and are not shared among other libraries. Commands issued by the
applications travel
to the library through three unique control paths. Thus, the data processing
for:

   - Department X is confined to the storage slots and drives in Logical
   Library A
   - Department Y is confined to the storage slots and drives in Logical
   Library B
   - Department Z is confined to the storage slots and drives in Logical
   Library C"