HP StorageWorks User Manual page 21

If you plan to use existing data in the external LU from the local disk array after mapping, you must
select the OPEN-V emulation type. For example, to migrate existing data in the external LU to the local
disk 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 LUN Security XP Extension is set for the
external LU on the external disk 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
• IO Suppression mode (Enable or Disable)
When mapping an LU, determine whether to suppress I/O operations from hosts (via the
XP12000/XP10000) to the mapped external LU.
If you select Enable, you can use the mapped LU only for Flex Copy XP operations.
If you select Disable, a host connected to the XP12000/XP10000 can use the mapped external LU as
if it is an LU inside the local disk array, but you cannot use the LU for Flex Copy XP 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 whether I/O from the host is propagated synchronously or asynchronously to the
external storage device.
If you select Enable, the local disk array signals the host that an I/O operation completed after
receiving the data into the local disk array's cache memory and then asynchronously destages the data
to the external disk array's cache where it is asynchronously destaged to disk.
If you select Disable, the local disk array signals the host that an I/O operation completed only after
the local disk array has synchronously written the data to the external disk array's cache. The external
disk array's cache then asynchronously destages this data to disk.
NOTE: Users should disable cache for low price/performance arrays, such as the HP MSA arrays.
The MSA array ports are slower than the XP FC ports. Disabling cache prevents applications that
use the MSA from consuming significant amounts of XP cache.
NOTE: All I/O to and from the local disk array in both cache modes always uses some amount of
cache. Write operations are always backed up in duplex cache. As an option, consider using the
XP Disk/Cache Partitioning feature as a recommended best practice for managing XP cache
consumption. Contact your HP account support representative for more information about
optimizing cache usage for external storage.
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 Cache LUN XP operations, you cannot use
the XP12000/XP10000 Cache LUN XP Bind mode. For more information, see the HP StorageWorks
Cache LUN XP user guide for XP12000/XP10000.
NOTE: If you set the emulation type of the mainframe system for the mapped LU, host I/O is
always propagated asynchronously to the external LU regardless of the Cache Mode setting.
• CLPR
When you use XP Disk/Cache Partition to partition cache memory, you must set the cache logical
partition (CLPR) used for accessing the mapped LU. You can also specify whether the CU selected at
mapping is restricted to the storage management logical partition (SLPR) the CLPR belongs to. For more
information about CLPRs and SLPRs, see the HP StorageWorks XP Disk/Cache Partition user guide.
operations" on page 32.
External Storage XP user guide 21