1. A cluster storage system comprising: a plurality of mass storage systems that provide storage capacity to store data blocks; middleware that provides a plurality of virtual storage pools for a plurality of users of the cluster storage system; at least one user interface configured to access the storage pool allocated to a user; wherein the middleware comprises at least one erase algorithm for secure erasure of data blocks; the at least one user interface provides an erase function to erase the storage pool allocated to the user; the middleware is configured to erase all user-allocated data blocks of the plurality of mass storage systems using the at least one erase algorithm and report the successful erasure via the user interface when the user calls up the erase function; and the cluster storage system is connected to the Internet and configured as a cloud storage system.