Capacity requirements for volumes

The capacity of an external volume is carved into LDEVs when mapped to the local system as an internal volume. You must be able to calculate the capacity that the internal volume will have.

Note the following information regarding internal and external volume capacity:

• The LDEV size in the internal volume varies according to the external system's emulation type.
• An external volume whose capacity is less than the minimum LDEV capacity cannot be used.
• An external volume with a capacity that is less than the base LDEV capacity for the emulation type can be used; this causes a custom-sized volume (CV) to be automatically created in the local system during mapping.
  • A custom volume in the local system has a minimum capacity, called minimum LDEV capacity.
  • Base LDEV capacity must be equal to or greater than the minimum LDEV capacity.

    The following figure illustrates minimum and base LDEV capacities.

    Minimum LDEV capacity and Base LDEV capacity are calculated with the following formulas.

    Minimum LDEV Capacity = Minimum Data Area Capacity
    + Control Information Area Capacity
    
    Base LDEV Capacity = Base Data Area Capacity
    + Control Information Area Capacity
    

    For mainframe systems volumes, other than 3390-A and 3390-V, capacities for the expanded control information area and the adjustment area are also necessary. For details, see Formula for calculating capacity for 3390-A and 3390-V mainframe volumes.

    If the external volume capacity is less than the minimum LDEV capacity, you cannot specify the emulation type.

  Idea of LDEV capacity:

  
  
  
  
  
• If you map an external volume that has a capacity that is higher than the base LDEV capacity for the emulation type, multiple LDEVs are created. The resulting LDEVs have the base LDEV capacity.
• You can create a maximum of 2,048 CVs.
• For emulation types other than OPEN-V, usable capacity in the internal volume is the capacity of the external volume minus control information area capacity.
• Data that exceeds the maximum capacity cannot be accessed.
• If you use a virtual volume for which Data Direct Mapping is enabled, you can map an external volume with more than 4 TB without changing its capacity as a virtual volume.

For details about mapping using virtual volumes for which Data Direct Mapping is enabled, see the Provisioning Guide.