By default a new install of Scan will have one warehouse (the initial one); a second warehouse can be created to supplement the first one if/when the first one runs out of space. Generally the full warehouse is locked, but remains active when additional warehouse are created.
This information can be found in the WarehousePath field in Impact.dbo.Warehouses, or by accessing the Warehouse Setup option in the application (Configure > System Setup).
Many clients would activate a smaller warehouse than the size of their tape backups; that way they can stop backing it up when it is locked. Other people may just lock it when it is nearly full, and add an additional warehouse. The other drives you have mapped are not setup in this application, and would not need to become active until that first warehouse is locked.
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