Calculating the maximum number of pairs

TrueCopy® User Guide
Version
9.8.7
Audience
anonymous
Part Number
MK-98RD9022-18

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, which must be calculated.
  • 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.
  1. Calculate the number of cylinders.
    1. Calculate the system's number of logical blocks, which is the volume capacity measured in blocks.
      Number of logical blocks = Volume capacity (bytes) / 512
    2. Calculate the number of cylinders.

      For OPEN-3, OPEN-8, OPEN-9, OPEN-E, OPEN-L, OPEN-K:

      Number of cylinders = ceil ( (ceil (Number of logical blocks / 96) ) / 15)

      For OPEN-V:

      Number of cylinders = ceil ( (ceil (Number of logical blocks / 512) ) / 15)

  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.

    For OPEN-3, OPEN-8, OPEN-9, OPEN-E, OPEN-L, OPEN-K, and OPEN-V:

    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 restricted by the following:
    • The number of bitmap areas required for TrueCopy (calculated above).
    • The total number of bitmap areas in the storage system. The number of bitmap areas is as follows:
      • VSP 5000 series: 65,536
      • VSP E series: 65,536
      • VSP G370, VSP G700, VSP G900, VSP F370, VSP F700, VSP F900: 65,536
      • VSP G350, VSP F350: 36,000

      Bitmap areas are also used by TrueCopy for Mainframe, Universal Replicator, Universal Replicator for Mainframe, and global-active device.

      Therefore, when you use these software applications together, reduce the number of bitmap areas for each software application from the total number of bitmap areas for the storage system before calculating the maximum number of pairs for TrueCopy in the following formula.

      Also, when TrueCopy and Universal Replicator, Universal Replicator for Mainframe share the same volume, regardless of whether the shared volume is primary or secondary, reduce the number of bitmap areas for each software application from the total number of bitmap areas for the storage system before calculating the maximum number of pairs for TrueCopy in the following formula. For more information on calculating the number of bitmap areas required for each software application, see the relevant user guide.

    Use the following formula:

    Maximum number of pairs = floor (Total number of bitmap areas in the storage system / Required number of bitmap areas)

    (VSP 5000 series) If the calculated maximum number of pairs exceeds the total number of LDEVs of the storage system, and the total number of LDEVs of the storage system is less than 65,280, then the total number of LDEVs of the storage system becomes the maximum number of pairs.

    (VSP E series, VSP G/F350, G/F370, G/F700, G/F900) Calculate the maximum number of pairs using the already calculated necessary number of bitmap areas and the number of bitmap areas in storage systems 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 control memory extended for TC.

    (VSP E series, VSP G350, G370, G700, G900, and VSP F350, F370, F700, F900)

    Extension status of control memory for TC

    Number of bitmap areas in storage systems

    Base (no Extension)

    Varies depending on the model:
    • VSP G350, VSP F350: 3,712
    • VSP G370, VSP G700, VSP F370, VSP F700: 36,000
    • VSP E series, VSP G900, VSP F900: 65,536

    With Extensions

    Varies depending on the model:
    • VSP G350, VSP F350: 36,000
    • VSP E series, VSP G370, VSP G700, VSP G900, VSP F370, VSP F700, VSP F900: 65,536