HP XP Racks - Manual (Page 15)

Enabled can adversely impact overall HP XP7 Storage performance if the I/O rate exceeds the
performance capabilities of the external system. If you specify Enabled, you should use the same
formula for sizing cache in both the internal and external systems.
A cache partition should be defined when Enabled is used for the Cache Mode setting. A CLPR
helps to protect overall HP XP7 Storage performance when the I/O rate tends to exceed the
capabilities of the external system.
Cache Mode effects with other HP software
Note the following additional effects regarding the Cache Mode setting:
•
If you perform the Cache Residency bind mode operation on an external volume, Cache Mode
is set to Enabled. In this case, twice as much cache capacity as user data area capacity is
required for the operation. (Bind mode is unavailable when Ext Stor Cache Mode is set to
Disable.)
•
The external volumes in a Thin Provisioning pool must all use the same Cache Mode setting,
either Enabled or Disabled.
•
Smart Tiers pool volumes require Cache Mode to be set to Enabled.
•
Data that is not written by the host (for example, data written by Business Copy) is
asynchronously destaged to the external storage system regardless of the Cache Mode setting.
•
When you set emulation type for a mainframe system, note the following:
Data written by a host using a Format Write command is asynchronously destaged to the
external storage system regardless of the Cache Mode setting. ◦
◦ Data written by a host using other Write commands are destaged to the external storage
system as configured in the Cache Mode setting.
Mainframe volumes
Note the following requirements and considerations for mapping mainframe external volumes:
•
Make sure that mainframe external volumes on a mainframe operating system consist of at
least one LDEV before mapping.
•
When multiple LDEVs exist in an external volume and numerous I/Os are made to them,
read/write commands may timeout. When the commands timeout, the SIM (21D2xx) is
reported.
•
Set the MIH (missing interrupt handler) timer to 45 seconds (which is the recommended value)
for mainframe external volumes on a mainframe operating system.
•
Pre-existing mainframe volumes on an external system that are accessed by FICON channels
cannot be mapped to the local storage system because HP XP7 Storage does not recognize
these volumes
You can prepare mainframe external volumes for mapping using one of the following methods:
◦ Zero-format the external volumes on the external system, map the volumes to HP XP7
Storage, then perform the Write to Control Blocks operation using Virtual LVI/Virtual LUN
on the local system side.
◦ Map the external volumes to HP XP7 Storage, and then format the mapped volumes on
the local storage system using the Virtual LVI/Virtual LUN.
Planning external volumes 15