HP XP Racks - Manual (Page 13)

Planning considerations for external storage systems
An external storage system’s performance is affected by local system operations; conversely,
performance of the host and local system are affected by the attributes assigned to the external
system.
Note the following regarding performance:
•
Host I/O performance (sequential write performance only) to mapped volumes can be improved
by setting SOM 872 to ON. For more information, call the HP Technical Support.
•
The performance and status of the external system affect read/write performance of the mapped
external volume. A heavy load on the external system slows the processing speed of read/write
operations. In this case, I/O from a mainframe host may receive a Missing Interrupt error.
•
If the host connected to the local storage system issues numerous I/O to be processed by the
external storage system, the commands from the host may time out.
•
When you execute HP XP7 Storage software commands that result in more I/O processed
than the external storage system can handle, the commands could time out and an error may
occur.
•
When you manipulate an external volume from the host, check the Path Blockade Watch time
for the external volume. If the value for this setting is longer than the timeout period of the host
command, the host command may time out when the power supply is off or when an error
occurs in the external storage system. If host I/O is a significant concern, make sure that the
Path Blockade Watch time of the external volume is the same as or shorter than the timeout
period of the host command.
Application performance considerations
Performance requirements for an application can be met when using external storage, but note
the following considerations in this regard:
•
Internal storage typically provides faster response times than external storage when the storage
is of the same type.
•
Storage used by the application must have the proper performance characteristics.
For example, SATA type storage does not provide the performance requirements usually
needed for an OLTP application.
•
The mainframe Transaction Processing Facility (TPF) should not use external storage.
Planning external volumes
External volumes must be set up to match External Storage requirements. Note the following:
•
You can use pre-existing data in an external volume after it is mapped to the local system,
with the following restrictions:
◦ Emulation type must be set to OPEN-V when you map the volume.
◦ To perform host I/O operations, an LU path from the Target port to the mapped volume
must be set.
•
An external volume’s maximum or minimum available capacity depends on the emulation
type you specify when mapping the volume.
See “Capacity requirements for volumes ” (page 16) for more information.
•
You cannot access data stored in an external volume beyond the allowed maximum capacity.
See “Maximum capacity of an external volume” in
“System requirements” (page 11) .
•
You cannot map an external volume whose capacity is smaller than the minimum capacity
required for internal volumes.
Planning considerations for external storage systems 13