HP XP P9000 for Compatible High Perf FICON Connectivity Software - Manual (Page 10)

Prestaging occurs under any of the following circumstances:
•
When prestaging is performed using Cache Residency.
•
When the storage system is powered on.
•
When cache maintenance is performed.
Figure 1 Cache Residency cache area
NOTE:
•
If the Cache Residency cache area is accessed for I/O before the prestaging operation is
complete, the data may not be available in cache at the first I/O access.
•
To prevent slow response times for host I/Os, the storage system may interrupt the prestaging
operation when the cache load is heavy.
•
Do not use the prestaging function if you specify the Cache Residency setting on a volume
during the quick formatting operation. To use the prestaging function after the quick formatting
operation completes, first release the Cache Residency setting and then specify the setting
again with the prestaging setting enabled. For information about quick formatting, see the HP
XP P9000 Provisioning for Open Systems User Guide or HP XP P9000 Provisioning for
Mainframe Systems User Guide.
•
When external volumes are configured in the storage system, you need to disconnect the
external storage system before powering off the storage system. If you power off the storage
system without performing the disconnect external storage system operation and then turn on
the power supply again, the prestaging process is aborted. If the prestaging process is aborted,
you need to perform the prestaging operation again.
The prestaging process is aborted if a volume is created, deleted, or restored during the
prestaging operation. If the prestaging process is aborted, you need to perform the prestaging
operation again after the create, delete, or restore volume operation is complete.
Priority mode (read data only)
In priority mode the Cache Residency extents are used to hold read data for specific extents on
volumes. Write data is write duplexed in cache other than Cache Residency cache, and the data
is destaged to the drives when disk utilization is low.
The required total cache capacity for priority mode (normal mode) is:
standard cache + Cache Residency cache + additional cache
The next table specifies the standard cache capacity requirements for priority mode operations.
Meeting these requirements is important for preventing performance degradation. For more
information about calculating cache size for priority mode, see
(page 69) .
10 Performance overview