HP XP7 Storage - Manual (Page 72)

5 Cache Residency Manager operations
This chapter provides instructions for managing data in cache using the Cache Residency Manager
software.
Overview of Cache Residency
Cache Residency enables you to store frequently accessed data in the storage system's cache
memory so that it is immediately available to hosts. Using Cache Residency you can increase the
data access speed for specific data by enabling read and write I/Os to be performed at the higher
front-end access speeds. You can use Cache Residency for both open-systems and mainframe data.
When Cache Residency is used, total storage system cache capacity must be increased to avoid
data access performance degradation for non-cache-resident data. The maximum allowable Cache
Residency cache area is configured when the cache is installed, so you must plan carefully for
Cache Residency operations and work with your HP representative to calculate the required amount
of cache memory for your configuration and requirements.
All write I/Os to Cache Residency data are duplex writes, guaranteeing full data integrity. The
Cache Residency data remains fixed in cache until you manually delete it. Deletion of Cache
Residency cache areas destages any write data to the affected volumes.
Cache Residency provides the following functions:
•
Priority cache mode
•
Bind cache mode
•
Prestaging data in cache
Priority mode (read data in cache)
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 drive 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
“Estimating cache size for Cache
Residency” (page 74) .
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 (read and write data in cache)
In bind mode the Cache Residency extents are used to hold read and write data for specific extents
on volumes, so both read and write speeds are improved. Data written to the Cache Residency
bind area is not destaged to the drives. To ensure data integrity, write data is duplexed in the
Cache Residency cache area, which consumes a significant amount of the Cache Residency cache.
72 Cache Residency Manager operations