Dark storage is allocated but unused storage capacity.
Although configured and mapped to servers, dark storage is not presented as file systems or volumes to users and applications. Furthermore, dark storage may not be detected by administrators, especially if servers and storage are managed by different people.
Dark storage is problematic for storage efficiency because although the capacity exists, it is not visible to users and doesn’t serve the enterprise. Storage utilization assessments are likely to be inaccurate, so it’s difficult for an administrator to know how much capacity is actually available.
A number of vendors offer storage management tools designed to detect dark storage and other utilization problems, such as unformatted and over-provisioned storage.