HP StorageWorks XP Remote Web Console Software - Manual (Page 15)

Cache LUN XP user guide for the XP10000/XP12000 15
NOTE: If a RAID-5 or RAID-6 volume area is changed from priority mode to bind mode and no cache is
added, only 33 percent of the user data fits into the area previously assigned for priority mode. The
remaining 67 percent is used to save read/write data. If a RAID-1 volume area is changed from priority
mode to bind mode and no cache is added, only 50 percent of the user data fits in the area previously
assigned for priority mode. The remaining 50 percent is used to save read/write data. Changing the
mode without cache extension requires Cache LUN XP reconfiguration.
Mainframe systems
To calculate the cache size for mainframe systems:
1. Calculate the converted values of the starting and ending addresses.
For specified LDEVs:
Setting value of ending address (CC) = (↓( (LDEV size Ч 15) - 1) ч 15↓)
Round down the calculated value between the two down arrows (↓) after the decimal point
Setting value of ending address (CC) is the value that is input to the operations box in the Cache
LUN pane)
Setting value of ending address (HH) = ( (LDEV size × 15) - 1) Mod15
Remainder is the setting value of ending address (HH)
Setting value of ending address (HH) is the value entered in the operations box on the Cache
LUN pane
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) are the values
entered in the operations box on the Cache LUN pane
For specified volumes:
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) are the values
entered in the operations box on the Cache LUN pane
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) are the values
entered in the operations box on the Cache LUN pane
2. Calculate the number of addresses between the starting and ending addresses 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 used by the user data
3. Calculate the required cache size according to the operation modes, or RAID levels, to use Cache
LUN XP.
a. Bind mode
RAID-1:
Required cache size = (Number of addresses Ч ( (128 Ч (512 + 16) ) Ч 2) ч 1,024
Units are KB
RAID types other than RAID-1:
Required cache size = (Number of addresses Ч (128 Ч (512 + 16) ) Ч 3) ч 1,024
Units are KB