HP XP Racks - Manual (Page 16)

NOTE: The following relates to mapped volumes:
◦ After the mapping operation, the status of the mapped volume becomes Blockade;
however, after the Write to Control Blocks operation is performed or mapped volume is
formatted on the local system, the mainframe host can then access the new mainframe
volume through the local HP XP7 Storage system's FICON channels.
◦ If you format the mapped volume from the external system, existing data is deleted and
there are no options for retaining it. This is the reason for formatting from the local system
side, as mentioned above.
For information on formatting and the Write to Control Blocks operations, see the HP XP7
Provisioning for Open Systems User Guide.
Open systems volumes
Note the following requirements and considerations for mapping OPEN systems external volumes:
•
OPEN systems external volumes do not require reformatting because the connection between
HP XP7 Storage and the external system is Fibre Channel.
However, if you need to initialize the data area for the volume, format the volume using the
Virtual LUN function. See the HP XP7 Provisioning for Open Systems User Guide for instructions.
•
OPEN-V emulation provides the most efficient use of storage and the best performance. Also,
emulation types other than OPEN-V may not retain existing data after being mapped.
External volume groups (ExGs)
During the mapping operation, you assign the external volume to an external volume group. This
allows you to organize external volumes used for similar purposes a group or groups.
For example, you may want to assign mapped volumes in the same external system to a specific
ExG. Or, you may assign volumes used in a particular function, such as Business Copy/Snapshot
or Continuous Access Journal, to an ExG, even if the data is stored in different external storage
systems.
You could also use ExGs to correspond to the external system’s physical disk grouping, such as a
RAID group.
You assign external volume group numbers during the mapping procedure.
Capacity requirements for volumes
An external volume's capacity is carved into LDEVs when mapped to the local system as an internal
volume. This topic provides information and instructions for calculating the capacity that the internal
volume will have.
Note the following regarding internal/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 can be used whose capacity is less than the base LDEV capacity for the
emulation type; 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 equal or be greater than the minimum LDEV capacity.
The following figure illustrates minimum and base LDEV capacities.
16 Requirements and planning