HP StorageWorks XP12000 User Manual - Page 13

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HP StorageWorks XP12000 User Manual

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.
In priority or bind mode, cache size is calculated with the assumption that one slot is the following:
•
Open-system volumes
For OPEN-V, one slot is 264 KB (512 LBAs)
For other than OPEN-V, one slot is 66 KB (128 LBAs)
•
zSeries and S/390 (3390) volumes
One slot is 66 KB (128 LBAs)
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
Cache LUN XP user guide for the XP10000/XP12000
13