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Considerations for HDAM databases

To compress an HDAM database, you must modify the DBD randomizing information before reloading the database to realize the DASD savings. Complete the following steps:

  1. Calculate HDAM parameters.Before compression, the DBD named DBD001 is defined with the following randomizing parameters:

    RMNAME=(DFSHDC40,10,1000,512)

    The number of RAPS in each block is 10, and the maximum RBN is 1,000.

    The PERCENT OF USED DASD SAVED field on the DPIDASD Space Estimation Utility Report is 66.4%.

    The following is an example of how to calculate the number of RAPs with compression:

    RAPS  = CURRENT RAPS/(1 - PERCENT DASD SAVED)
     = 10/(1 - .664)
     = 10/.336
     = 29

    RAA   = CURRENT RAA * (1 - PERCENT DASD SAVED)
     = 1000 (1 - .664)
     = 1000 (.336)
     = 336

    bytes = CURRENT bytes * (1 - PERCENT DASD SAVED)
     = 512 (1 - .664)
     = 512 (.336)
     = 173

    The new randomizing parameters for DBD001 are as follows:

    RMNAME=(DFSHDC40,29,336,173)

    The total number of RAPS in the RAA does not change with compression. However, with compression more RAPS can fit in a single block, so the total number of blocks needed is less. To force into overflow the same segments that are currently in overflow, decrease the maximum bytes amount by the percent of DASD saved.

  2. Modify your DBD parameters.Using the values calculated, modify the test copy of the DBD.

Related topic

Compression-of-full-function-databases


 

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