HP StorageWorks External Storage XP user guide for the XP12000, XP10000, SVS200 (T1706-96009, October 2007)

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 Flex Copy XP 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 LUN Security XP Extension 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
(andtheoriginaldatamustbeconsideredlost).Formoreinformationaboutvolumecapacity,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 Flex Copy XP 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 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 if I/O from the host is propagated synchronously or asynchronously to the
external storage device. All I/O to and from the local array in both cache modes always uses some
amount of 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's cache where it is asynchronously destaged to disk.
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's cache. The external 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:
As an option, consider using XP Disk/Cache Partition as a recommended best practice for managing
XP cache consumption. See Managing cache with external storage or 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 Cache LUN XP Bind mode. For more information, see the HP StorageWorks Cache LUN XP
user guide for XP12000/XP10000/SVS200.
External Storage XP user guide
23