A compound resource allows the SRB to function as a complete (although basic) archival storage system (also known as an hierarchical storage system (HSM)). A compound resource may be configured to contain a pool of cache resources and a tape resource. When a user creates a file using a compound resource, the object created becomes a "compound object". The actual data of a "compound object" may reside on cache or tape or both. Unlike the SRB replica, a "compound object" always appears as a single object even though there may be multiple copies of the data. It is a simple hierarchical system where data migrate automatically between cache and tape. Data is always staged on cache automatically whenever it is accessed and migrates to tape by the system administrator when more cache space is needed. The cache and tape resources can be distributed across a WAN.