Storing data volumes in virtual and physical address spaces such that the data units are contiguous in virtual address space but fragmented in physical address space. The mapping between virtual and physical address space is managed by a storage controller that is configured to implement deletes reversibly with a so-called soft delete, the soft delete being reversible up to a later permanent or hard delete. A soft delete triggers a compaction in which the data units of the to-be-deleted volume are gathered together in physical address space. During the time between compaction and hard delete (or restore), the soft deleted volume is thus stored in a space efficient manner. Moreover, the subsequent hard delete can be performed more quickly than if the soft deleted volume were still fragmented across physical address space freeing up space quicker.