A volume group specifies a set of logical volumes. By identifying different volume groups for different uses (for example, SCSI target, FICON control unit, Remote Mirror and Copy secondaries, FlashCopy targets, Copy Services), access to the set of logical volumes that are identified by the volume group can be controlled.
A volume map specifies a set of logical volume numbers as a list of 2 byte logical volume numbers. The configured logical volumes have consecutive locations in the list starting from the beginning. An unconfigured entry is indicated by a X'FFFF' logical volume number. You can specify a maximum of 256 logical volumes (512 bytes). A volume mask specifies a set of logical volume numbers as a bitmap with one bit per logical volume number. A configured logical volume is indicated by a B'1'. A maximum of 65280 (63.75 KB) logical volumes can be specified (8 KB).
You can configure a CKD base address in one or more volume groups. A CKD alias address can be configured in one and only one volume group and the base address that it is associated with must be present in that volume group. The CKD alias can also be reassigned to a base address that is present within its assigned volume group. A CKD base address can be removed from a volume group if there are no alias addresses in the volume group that are associated with the base address. A CKD alias address can be removed from a volume group by deconfiguring the alias.
If an access attempt encounters an unconfigured logical volume number in the volume group, the access is treated as an access to an unconfigured logical volume. Requests to add additional volume group definitions or to add additional logical volume numbers to an existing volume group definition are rejected if the definition does not fit in the space that is allocated for volume group definitions.