Cache Residency Cache Areas; Cache Size Requirements; Calculating Cache Size For Open Systems - HPE XP7 User Manual

Cache Residency cache areas

For OPEN-V volumes, the resident cache areas are defined in logical blocks using logical block
addresses (LBAs), with a minimum size of 512 LBAs (equivalent to 264 KB). In most cases you
will assign an entire open-systems volume for cache residency.
For mainframe volumes, the resident cache areas are defined on contiguous tracks with a
minimum size of one cache slot (or track) (equivalent to 66 KB) and a maximum size of one LVI.
If desired, you can prestage the data to the resident cache area. If prestaging is not used, the
data is loaded into the resident cache area when the first "miss" occurs. If prestaging is used,
performance may be affected while the data is read into resident cache.
CAUTION:
not be performed during peak activity.
The Cache Residency cache areas are dynamic and can be added and deleted when adding or
removing cache memories. If you need to expand the amount of Cache Residency cache without
canceling the existing settings, contact HPE technical support.

Cache size requirements

The required cache size for using Cache Residency depends on several factors including cache
residency mode (bind or priority), RAID level, and use of external storage. For example, if bind
mode is used, RAID1 storage systems require twice the cache size for the Cache Residency
data, whereas RAID5 and RAID6 storage systems require three times the cache size. If external
volumes are used, twice the cache size is required for the Cache Residency data.
If priority mode or bind mode is used, the cache size is calculated assuming that one slot has
the following values.
For open-systems volumes:
◦
For OPEN-V, one slot is 264 KB (512 LBAs).
◦
For other than OPEN-V, one slot is 66 KB (128 LBAs).
For mainframe (3390) volumes:
◦
One slot is 66 KB (128 LBAs).

Calculating cache size for open systems

You can calculate cache size for open systems.
Prestaging of data into resident cache may impact host I/O performance and should
Estimating cache size for Cache Residency 141