HP XP P9500 Storage - Manual (Page 41)

Calculating cache size for mainframe systems
1. Calculate the converted values of the starting address and the ending address.
a.
For all specified LDEVs:
Setting value of ending address (CC) = floor (((LDEV size Ч 15) - 1) ч 15)
Round down the value that is calculated from the formula enclosed by floor(). "Setting
value of ending address (CC)" is the value which is input on the Cache Residency window.
Setting value of ending address (HH) = ((LDEV size × 15) - 1) Mod 15
The remainder will be the setting value of ending address (HH).
"Setting value of ending address (HH)" is the value which is input on the Cache Residency
window.
Converted value of starting address = 0
Converted value of ending address = Setting value of ending address (CC) × 15 + Setting
value of ending address (HH)
"Setting value of ending address (CC)" and "Setting value of ending address (HH)" is
the value which is input on the Cache Residency window.
b. If the volumes are specified:
Converted value of starting address = Setting value of starting address (CC) × 15 +
Setting value of starting address (HH)
"Setting value of ending address (CC)" and "Setting value of ending address (HH)" is
the value which is input on the Cache Residency window.
Converted value of ending address = Setting value of ending address (CC) × 15 + Setting
value of ending address (HH)
"Setting value of ending address (CC)" and "Setting value of ending address (HH)" is
the value which is input on the Cache Residency window.
2. Calculate the number of addresses between the starting address and the ending address
calculated in step 1:
Number of addresses = Converted value of ending address - Converted value of starting
address + 1
Calculate the number of addresses of cache that are used by the user data.
3. Calculate the required cache size according to the operation modes, or the RAID levels to use
Cache Residency.
a.
Where the bind mode is set:
For RAID1
Required cache size = (Number of addresses Ч ((128 Ч (512 + 16)) Ч 2) ч 1,024
The unit is KB.
b. Where the priority mode is set:
Required cache size = (Number of addresses Ч (128 Ч (512 + 16))) ч 1,024
The unit is KB.
Cache Residency extents
The Cache Residency cache areas (called cache extents) have the following parameters:
•
The cache extents are dynamic and can be added and deleted at any time.
•
The P9500 supports a maximum of 4,096 cache extents per LDEV and 16,384 cache extent
per storage system.
Calculating cache size for mainframe systems 41