HP XP P9500 Storage - Manual (Page 14)

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Make sure that a mapped external volume is accessed only from the local HP P9500 storage
system.
◦ Make sure that a mapped external volume is not accessed from a host that is connected
to the external storage system.
◦ Make sure that a mapped external volume is not manipulated by a copy function or any
other functions of the external storage system.
◦ Accessing a mapped external volume from the external storage system requires that the
volume mapping be disconnected first.
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External volumes that are reserved by a host cannot be mapped as internal volumes. To map
these volumes, cancel the reserve settings, remove host access to the volumes, and then perform
the mapping operation.
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Do not map multi-platform volumes of external storage systems as internal volumes.
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When an external storage system that uses control unit path ownership is connected to the
HP P9500, configure the external path to the primary controller in the external storage system
as the primary path.
Ownership is the exclusive right to control volumes. A controller that has ownership is called
a primary controller. If the external path is connected to a controller that does not have
ownership, and the path is configured as primary path, the ownership will be transferred,
which may affect performance.
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A management LU cannot be used as an external volume.
A management LU receives commands from an application; it controls or manages the
application, and stores control information from the application. An example of a management
LU is a Universal Xport LU. (A RAID Manager command device is not a management LU.)
Before performing the external volume mapping operation, perform one of the following
operations on the external storage system.
◦ Delete the management LU from the port to be connected to the HP P9500.
◦ Make sure that at least one LU is used for data storage and has a smaller LUN (LU number)
than the management LU’s LUN. Also make sure that the data storage LU is set to the port
connected to the HP P9500.
◦ Use the security function and configure the access attribute of the management LU to
prohibit read and write operations.
An external storage system that has a management LU might not be recognized by the local
storage system.
Cache use and external storage performance
Performance for external storage used with the HP P9500 is highly dependent on proper cache
configuration. The Cache Mode setting, which you specify during the mapping operation, affects
external storage performance.
When data is written to the mapped external volume, Cache Mode controls when the write-complete
response is sent to the host.
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When Enabled is specified, the write-complete response is sent when the write data is in the
HP P9500 cache.
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When Disabled is specified, the write-complete response is sent when the write data is accepted
by the external system.
Disabled is the safest setting and is recommended when there is a possibility that the I/O rate will
exceed the short term capabilities of the external storage.
14 Requirements and planning