HP XP P9000 for Compatible High Perf FICON Connectivity Software - Manual (Page 9)

Upper-limit control
Using Performance Control you can limit the number of I/O requests from servers to the storage
system as well as the amount of data that can be transferred between the servers and the storage
system to maintain production server performance at the required levels. This practice of limiting
the performance of low-priority host servers is called upper-limit control.
Threshold control
While upper-limit control can help production servers to perform at higher levels during periods
of heavy use, it may not be useful when production servers are not busy. For example, if the I/O
activity from production servers is high between 09:00 and 15:00 hours and decreases significantly
after 15:00, upper-limit control for development servers may not be required after 15:00.
To address this situation Performance Control provides threshold control, which automatically
disables upper-limit control when I/O traffic between production servers and the storage system
decreases to a user-specified level. This user-specified level at which upper-limit control is disabled
is called the threshold. You can specify the threshold as an I/O rate (number of I/Os per second)
and a data transfer rate (amount of data transferred per second).
For example, if you set a threshold of 500 I/Os per second to the storage system, the upper-limit
controls for development servers are disabled when the I/O rate of the production servers drops
below 500 I/Os per second. If the I/O rate of the production servers goes up and exceeds 500
I/Os per second, upper-limit control is restored to the development servers.
If you also set a threshold of 20 MB per second to the storage system, the data transfer rate limit
for the development servers is not reached when the amount of data transferred between the storage
system and the production servers is less than 20 MB per second.
Cache Residency overview
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.
Cache Residency provides the following functions:
•
Prestaging data in cache
•
Priority cache mode
•
Bind cache mode
Once data has been placed in cache, the cache mode cannot be changed without cache extension.
If you need to change the cache mode without cache extension, you must release the data from
cache, and then place the data back in cache with the desired mode.
Prestaging data in cache
Using Cache Residency you can place specific data into user-defined Cache Residency cache
areas, also called cache extents, before it is accessed by the host. This is called prestaging data
in cache. When prestaging is used, the host locates the prestaged data in the Cache Residency
cache during the first access, thereby improving data access performance. Prestaging can be used
for both priority mode and bind mode operations.
Cache Residency overview 9