HP StorageWorks XP Remote Web Console Software - Manual (Page 18)

The following are the external LU's attributes:
•
Emulation type
Set the mapped LU's emulation type by selecting any emulation type from the drop-down list.
However, if you plan to use the mapped LU for XP Flex Copy operations, or you plan to access
existing data in the external LU, you must select the OPEN-V emulation type to avoid data
resizing.
If you plan to use existing data in the external LU from the local array after mapping, you must
select the OPEN-V emulation type. For example, to migrate existing data in the external LU to
the local array volume, you must set the OPEN-V emulation type when mapping the external
LU.
You must also select the OPEN-V emulation type when VMA of HP XP LUN Security Extension
Software is set for the external LU on the external array side.
If you select an emulation type other than OPEN-V, additional space is taken for XP
management information. This means that after mapping, LU capacity is less than the actual
external LU capacity (and the original data must be considered lost). For more information
about volume capacity, see
Limitations on External Storage XP operations .
•
IO Suppression mode (Enable or Disable)
When mapping an LU, determine whether to suppress I/O operations from hosts (via the local
array) to the mapped external LU.
If you select Enable, you can use the mapped LU only for XP Flex Copy operations.
If you select Disable, a host connected to the local array can use the mapped external LU as
if it were an LU inside the local array, but you cannot use the LU for XP Flex Copy operations.
You can select Enable only when you set the OPEN-V emulation type for the mapped LU.
When you set an emulation type other than OPEN-V, the IO Suppression mode is automatically
set to Disable.
•
Cache Mode (Enable or Disable)
Cache mode specifies if I/O from the host is propagated synchronously (Disable) or
asynchronously (Enable) to the external storage device. By default cache mode is set to Enable.
All I/O to and from the local array in both cache modes always uses cache. Write operations
are always backed up in duplex cache.
If you select Enable, the local array signals the host that an I/O operation completed after
receiving the data into the local array's cache memory, and then asynchronously destages
the data to the external array.
If you select Disable, the local array signals the host that an I/O operation completed only
after the local array has synchronously written the data to the external array.
When IO Suppression mode is set to Enable, Cache Mode changes by default to Disable.
If you use an external LU and set Cache Mode to Disable for HP XP Cache LUN Software
operations, you cannot use the XP Cache LUN Bind mode. For more information, see the HP
XP Cache LUN user guide for XP12000/XP10000 Disk Arrays and SVS 200.
18 Preparing for XP External Storage operations