HP XP Cache LUN Software - Manual (Page 13)

Cache LUN XP user guide for the XP12000/XP10000/SVS200 13
Bind mode and RAID groups
To change a RAID-1, RAID-5, or RAID-6 parity group’s mode from priority mode to bind mode, reset and
re-allocate the affected Cache LUN XP extent. When you re-allocate, specify the greater capacity needed
for bind mode.
Pre-staging
As mentioned before, data assigned to a Cache LUN XP cache extent becomes resident (“staged”) in
cache after it is first accessed by the host. Then, the host finds the data in cache for the second and
subsequent accesses. The pre-staging function puts data in cache before the first read. Therefore,
pre-staging allows the host to find data in cache on the first access.
Specify pre-staging when you set up the cache extent. You can use this function with either priority or bind
mode.
You cannot change a Cache LUN XP extent after it is configured. To change the specification, you must
reset (“release”) the Cache LUN XP extent, and then re-allocate (“set”) the Cache LUN XP extent.
Required cache size for Cache LUN XP
The required cache size for Cache LUN XP depends on the operation modes. For example, in bind mode,
RAID-1 groups require twice the cache size for user data to use Cache LUN XP. However, RAID-5 or RAID-6
groups require three times the cache size for user data to use Cache LUN XP.
NOTE: When external volumes are used, twice the cache size is required for user data to use Cache
LUN XP.
The following sections describe the calculation procedures for each operation mode and RAID level.
Open systems
To calculate the cache size for open systems:
1. Calculate the converted values of the starting and ending addresses.
For specified LDEVs:
a. OPEN-V
Number of LBAs = LDEV size (KB) × 2
Convert LDEV size to number of LBAs
Number of slots = (↑Number of LBAs ÷ 512↑)
Round up the calculated value between the two up arrows (↑) after the decimal point
Converted value of starting address = 0
Converted value of ending address = (Number of slots × 512) - 1
b. Emulation types other than OPEN-V
Number of LBAs = LDEV size (KB) × 2
Convert LDEV size to number of LBAs
Number of slots = (↑Number of LBAs ÷ 96↑)
Round up the calculated value between the two up arrows (↑) after the decimal point
Converted value of starting address = 0
Converted value of ending address = (number of slots × 96) - 1
For specified volumes:
a. OPEN-V
Starting value = (↓Setting value of starting address (LBA) ÷ 512↓)
Round down the calculated value between the two down arrows (↓) after the decimal point
Setting value of starting address (LBA) is the value entered in the operations box on the Cache
LUN pane