When media files within an account must internally be split into different "buckets", new media libraries should be created.
This allows for example:
All media libraries share your account's storage quota. Team members can be given access to multiple media libraries.
An account with two websites and three media libraries
Each media library has its own:
Websites and media libraries are fully independent. It is possible to publish to the same website gallery from multiple media libraries.
On the gallery's admin page: