HP XP P9500 Storage - Manual (Page 36)

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For the external volume, for which the Cache Mode is set to Disable, the bind mode for the
Cache Residency operation is not available.
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If you use the mapped external volume for the Cache Residency operation and set the bind
mode, the cache of twice as much capacity as the user data is required for the Cache Residency
operation.
Creating LUSE volume guidelines
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LUSE is not supported with mainframe volumes.
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Do not combine LDEVs of multiple external volumes to create a LUSE volume. Only LDEVs in
the same external volume can only be used as LUSE volumes.
When you combine LDEVs of multiple external volumes to create a LUSE volume, the following
problems will occur:
◦ If a LUSE volume consists of multiple external volumes and one external volume has lower
performance than the other volumes, the lower performance of the volume affects the
performance of the LUSE volume.
◦ When an external volume that is a component of a LUSE volume is blocked, data reliability
of the LUSE volume will deteriorate because the LUSE volume has both accessible area
and inaccessible area from a host.
◦ When you disconnect an external volume or resume the use of an external volume, you
need to perform the operation at the same time on all the external volumes that are
components of the LUSE volume.
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The mapped volumes that have different cache mode settings cannot be used to create one
LUSE volume.
Maintenance guidelines for an external storage system
Before you change settings of the external storage system, you must delete the external volume
mapping. After you change settings of the external storage system, you must remap the external
volume. If you do not remap the volume, the external volume cannot be used in the local storage
system. The examples of external storage system settings requiring the remapping of external
volume are as follows:
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Changing WWNs of target ports that connect to the local storage system
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Changing the serial number of the external storage system
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Changing LUNs of volumes of the external storage system
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Reducing the volume capacity of the external storage system so that the volume capacity is
smaller than when volume mapping was performed
Besides, remapping is required for External Storage after you change external storage system
settings that require modification on the host side when hosts are connected directly to a external
storage system.
Before you delete the external volume mapping, make sure that the volume has no LU paths, and
that the volume is not a component of any pairs (such as Continuous Access Synchronous pairs).
Performance and status guidelines
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The performance and status of the external storage system affect the Read and Write
performance of the mapped external volume. If there is a heavy load on the external storage
36 Prerequisites