Cache Residency Operations; Overview Of Cache Residency; Priority Mode (Read Data In Cache); Bind Mode (Read And Write Data In Cache) - HPE XP7 User Manual

6 Cache Residency operations

This chapter provides instructions for managing data in cache using Cache Residency.

Overview of Cache Residency

Cache Residency enables you to retain 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 Hewlett Packard Enterprise 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
Residency" (page
Table 24 Cache capacity requirements for CR priority mode
Settings of priority mode
Specified number of cache areas is 8,192 or less and the specified
capacity is 128 GB or less
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.
138 Cache Residency operations
140).
"Estimating cache size for Cache
Standard cache capacity
16 GB
32 GB