On demand only storage unit setting
The On demand only storage unit setting specifies whether the storage unit is available exclusively on demand - that is, only when a policy or schedule is explicitly configured to use this storage unit. Uncheck to make the storage unit available to any policy or schedule.
Note:
If On demand only is selected for all storage units, be sure to designate a specific storage unit for each policy or schedule. Otherwise, NetBackup is unable to find a storage unit to use.