HP XP7 Storage - Manual (Page 25)

Calculating maximum number of pairs
NOTE: In the calculations below, note the following:
•
ceil () indicates that the value between the parentheses should be rounded up to the nearest
integer.
•
Number of logical blocks indicates volume capacity measured in blocks.
Number of logical blocks - Volume capacity (in bytes) / 512
To calculate the number of cylinders
Use the following formula:
Number of cylinders = (ceil ( (ceil (number of logical blocks / 512))
/ 15))
To calculate the number of required bitmap areas:
Use the following formula
ceil((number of cylinders x 15) / 122,752) )
where:
•
number of cylinders x 15 indicates the number of slots
•
122,752 is the number of slots that a bitmap area can manage
NOTE: Doing this calculation for multiple volumes can result in inaccuracies. Perform the
calculation for each volume seperately, then total the bitmap areas. The following examples
show correct and incorrect calculations. Two volumes are used: one of 10,017 cylinders and
another of 32,760 cylinders
Correct calculation
ceil ((10,017 x 15) / 122,752) = 2
ceil ((32,760 x 15) / 122,752) = 5
Total: 7
Incorrect calculation
10,017 + 32,760 = 42,777 cylinders
ceil ((42,777 x 15) / 122,752) = 6
To calculate the maximum number of pairs
The maximum number of pairs is determined by the following:
•
The number of bitmap areas required for Continuous Access Journal (calculated above).
•
The total number of bitmap areas in the storage system, which is 65,536.
Bitmap areas reside in an additional shared memory, which is required for Continuous Access
Journal.
◦ Bitmap areas are used not only by Continuous Access Journal, but also by Continuous
Access Journal Z, Continuous Access Synchronous, and Continuous Access Synchronous
Z. Therefore, the number of bitmap areas used by these other program products (if any)
Planning pair volumes 25