Computer systems, virtual storage systems, and virtual storage system operational methods are described. According to one aspect, a computer system includes a virtual storage system including a physical storage space, a virtual storage space, and a non-guaranteed available capacity utilized to generate a non-guaranteed snapshot volumes of virtual storage volumes of the virtual storage space, wherein the virtual storage system is configured to monitor the non-guaranteed available capacity and to present a report regarding the non-guaranteed available capacity responsive to the monitoring and a host configured to execute an application wherein generation of a non-guaranteed snapshot volume of at least one of the virtual storage volumes is desired, to access the report to determine the non-guaranteed available capacity, and to issue a request to the virtual storage system to generate the at least one non-guaranteed snapshot volume of the at least one virtual storage volume responsive to the accessing.