Estimating the virtual storage allocated at an installation is important primarily because this storage must be backed up by central storage in some ratio (for example, 25%). This backup storage contributes significantly to an installation's total central storage requirements.

Virtual storage must also be backed by auxiliary storage. For information about estimating the amount of storage your installation will need, see the discussion of paging data space in Auxiliary storage management initialization.

Each installation can use virtual storage parameters to specify how certain virtual storage areas are to be allocated. These parameters have an impact on central storage use and overall system performance. The following overview describes the function of each virtual storage area. For information about identifying problems with virtual storage requests, see Identifying problems in virtual storage (DIAGxx parmlib member).