HP XP7 Storage - Manual (Page 75)

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: Prestaging of data into resident cache may impact host I/O performance and should
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 HP 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.
Estimating cache size for Cache Residency 75