HP XP P9000 for Compatible High Perf FICON Connectivity Software - Manual (Page 14)

NOTE:
•
If you access the Cache Residency area for input and output before the prestaging operation
is performed from the SVP or Remote Web Console, the host may not be able to find data in
the cache at the first I/O access after Cache Residency is configured.
•
To prevent the slow response time of the host I/O, the prestaging operation may be interrupted
when the cache load is heavy.
•
If you specify the Cache Residency setting on the volume during the quick formatting, do not
use the prestaging function. If you want to use the prestaging function after the quick formatting
processing completes, first release the setting and then specify the Cache Residency setting
again, with the prestaging setting enabled. For information about the quick formatting, see
HP XP P9000 Provisioning for Open Systems User Guide or HP XP P9000 Provisioning for
Mainframe Systems User Guide.
•
When external volumes are set in the storage system, execute the disconnect external storage
system operation to the external storage system before turning off the power supply of the
storage system. If you turn off the power supply of the storage system without executing the
disconnect external storage system operation to the external storage system and then turn on
the power supply again, the prestaging processing is aborted. If the prestaging processing is
aborted, perform the prestaging operation from SVP or Remote Web Console.
The prestaging processing is aborted if a volume is created, deleted, or restored during the
prestaging operation. If the prestaging processing is aborted, perform the prestaging operation
from SVP or Remote Web Console after finishing a volume create, delete, or restore volume
operation.
Priority mode
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 that of Cache Residency, and the data
is destaged to the disk drive when disk utilization is low.
In priority mode (normal mode), the total capacity of cache required is:
standard cache + Cache Residency cache + additional cache
The following table specifies the standard cache capacity requirements for Cache Residency priority
mode operations. Meeting these requirements is important for preventing performance degradation.
For more information about calculating cache size for priority mode, see
“Estimating cache size”
(page 69) .
Table 3 Cache capacity requirements for CR priority mode
Standard cache capacity Settings of priority mode
16 GB Specified number of cache areas is 8,192 or less
and the specified capacity is 128 GB or less
32 GB Specified number of cache areas exceeds 8,192
or the specified capacity exceeds 128 GB
1 GB = 1,073,741,824 bytes
Bind mode
Cache Residency uses extents to hold read and write data for specific extents on volumes. Data
written to the Cache Residency bind area is not destaged to the disk. To ensure data integrity,
write data is duplexed in the Cache Residency area, which consumes a significant amount of the
Cache Residency cache.
14 About performance monitoring