Calculating the maximum number of pairs

True Copy User Guide for VSP One Block
Version
10.5.x
Audience
anonymous
Part Number
MK-23VSP1B020-06
ft:lastEdition
2026-05-04

The maximum number of pairs you can have in a single storage system is based on the following:

  • Storage system model
  • Number of cylinders in the volumes, which must be calculated
  • Number of bitmap areas required for a TrueCopy volume

    This is calculated using the number of cylinders.

Note:

Bitmap areas are not used for volumes larger than 4,194,304 MB (8,589,934,592 blocks). Therefore, you do not need to calculate the maximum number of pairs when creating a TC pair with a DP-VOL that is larger than 4,194,304 MB (8,589,934,592 blocks).

  1. Calculate the number of cylinders.
    1. Calculate the number of logical blocks in the storage system, which is the volume capacity measured in blocks.
      number-of-logical-blocks = volume-capacity-in-bytes / 512
    2. Calculate the number of cylinders.

      number-of-cylinders = ceil ( (ceil (number-of-logical-blocks / 512) ) / 15)

      For ceil(), round up the result within the parentheses to the nearest whole number.

  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 × 15) / 122,752)

    Note:

    Performing 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 volume of 10,017 cylinders, and another volume of 32,760 cylinders

    Correct calculation

    ceil ((10,017 × 15) / 122,752) = 2

    ceil ((32,760 × 15) / 122,752) = 5

    Total: 7

    Incorrect calculation

    10,017 + 32,760 = 42,777 cylinders

    ceil ((42,777 × 15) / 122,752) = 6

    Total: 6

  3. Calculate the maximum number of pairs, which is based on the following:
    • Number of bitmap areas required for TrueCopy (calculated above)
    • Total number of bitmap areas
      • VSP One B85: 65,536
      • VSP One B20 series: 65,536
      • VSP E series: 65,536
      • VSP G/F370, G/F700, G/F900: 65,536
      • VSP G/F350: 36,000

      Bitmap areas are also used by Universal Replicator and global-active device. Therefore, when you use these software applications together, subtract the number of bitmap areas for each software application from the total number of bitmap areas before calculating the maximum number of pairs for TrueCopy.

      Also, when TrueCopy and Universal Replicator share the same volume, regardless of whether the shared volume is the P-VOL or the S-VOL, subtract the number of bitmap areas for each software application from the total number of bitmap areas before calculating the maximum number of pairs for TrueCopy. For details about calculating the number of bitmap areas for other software products, see the documentation for the software product.

    Use the following formula to calculate the maximum number of pairs:

    maximum-number-of-pairs = floor (total-number-of-bitmap-areas-in-the-storage-system / required-number-of-bitmap-areas)

    Maximum number of TC pairs:

    • VSP One B24: 16,384
    • VSP One B26: 32,768
    • VSP One B28: 49,152
    • VSP One B85: 65,280

    Subtract the number of command devices (including virtual command devices) from the maximum number of TC pairs.

    Calculate the maximum number of pairs using the calculated required number of bitmap areas and the number of bitmap areas in the storage system as listed in the following table. The number of bitmap areas in a storage system is determined by the storage system model and the availability of shared memory extended for TC.

    Extension status of shared memory for TC

    Number of bitmap areas in the storage system
    Base (no Extension) 65,536
    With Extensions VSP One B26, VSP One B28VSP One B85: 65,536