HP XP Array Manager Software - Manual (Page 7)

on storage systems configured with at least 512 MB of cache. Your HP service representative
configures the maximum allowable Cache Residency area when the cache is installed.
Cache Residency Modes
Cache Residency provides the following two operational modes for storing user data in cache
memory:
•
“Priority Mode” (page 7)
•
“Bind Mode” (page 7)
•
“Changing from Priority Mode to Bind Mode” (page 8)
Priority Mode
In Priority Mode (normal mode), the total capacity of cache required is:
Standard cache + Cache Residency cache + Additional cache
The main advantage of Cache Residency priority mode is that read data is transferred at host data
transfer speed. 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 and the
data is de-staged to the disk drive when disk utilization is low. You can set the priority mode from
the operations box on the lower right of the Cache Residency window (see
“Operations Box
(open-systems LDEV selected)” (page 27) or “Operations Box (mainframe LDEV selected)” (page 27) ).
Table 1 (page 7) lists the standard cache capacity values for priority mode operations. For further
information on the calculating procedures of required cache size for using Cache Residency if the
priority mode is set, see
“Required Cache Size for Cache Residency” (page 11) .
Table 1 Standard Cache Capacity Required to Prevent the Access Performance from Degrading
Standard Cache Capacity Number of Areas Set in Priority Mode
2,048 MB×2 1 to 4096
4,096 MB×2 4097 to 8192
6,144 MB×2 8193 to 12288
8,192 MB×2 12289 to 16384
Bind Mode
In Bind Mode, the total capacity of cache required is:
Standard cache + Cache Residency cache
In bind mode, the Cache Residency extents are used to hold read and write data for specific
extent(s) on volume(s). Any data written to the Cache Residency bind area is not de-staged 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. You can set the bind mode from the operations
box on the lower right of the Cache Residency window (see
“Operations Box (open-systems LDEV
selected)” (page 27) or “Operations Box (mainframe LDEV selected)” (page 27) ). For further
information on the calculating procedures of required cache size for using Cache Residency if the
bind mode is set, see
“Required Cache Size for Cache Residency” (page 11) .
Table 2 (page 8) lists the standard cache capacity values for priority mode operations. For further
information on the calculating procedures of required cache size for using Cache Residency if the
priority mode is set, see
“Required Cache Size for Cache Residency” (page 11) .
The primary advantage of bind mode is that all targeted read and write data is transferred at host
data transfer speed. In addition, the accessibility of read data is the same as Cache Residency
Cache Residency Modes 7