Calculating Maximum Number Of Pairs - Hitachi G200 User Manual

The maximum number of TC pairs depends on the number of LDEVs, not the
number of LUs.

Calculating maximum number of pairs

It is necessary to calculate the maximum number of pairs you can have on
the storage system. The maximum number is based on the following:
• The number of cylinders in the volumes.
• The number of bitmap areas required for a TrueCopy volume, which is
calculated using the number of cylinders.
If the volume size is larger than 4,194,304 MB (8,589,934,592 blocks),
the bitmap area is not used. Therefore, you do not need to calculate the
maximum number of pairs when creating TC pairs with a DP-VOL whose
size is larger than 4,194,304 MB (8,589,934,592 blocks).
Note: In the following formulas: for ceil(), round up the result within the
parentheses to the nearest integer, and for floor(), round down the result
within the parentheses to the nearest integer.
To calculate the maximum number of pairs
1 Calculate the number of cylinders.
.
a
.
b
.
2 Calculate the number of bitmap areas per volume.
.
In the following calculation, differential data is measured in bits. 122,752
bits is the amount of differential data per bitmap area.
Number of bitmap areas = ceil ( (Number of cylinders x 15) /
122,752)
Note: Doing this calculation for multiple volumes can result in
inaccuracies. Perform the calculation for each volume separately, and
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
Total: 6
Hitachi TrueCopy® User Guide for Hitachi Virtual Storage Platform Gx00 and Fx00 Models
Calculate the system's number of logical blocks, which is the volume's
capacity measured in blocks.
Number of logical blocks = Volume capacity (bytes) / 512
Calculate the number of cylinders:
Number of cylinders = ceil ( (ceil (Number of logical
blocks / 512) ) / 15)
Planning for TrueCopy
3-13