Example of an OCDS calculation

In this example, the work sheet in Figure 1 and the following assumptions are used to calculate how many cylinders are needed for the OCDS.

1. Assuming that you are using extended TTOCs and that 200 000 mds + (nds × bver) is the total number of backup data set versions and migration data set copies on tape at your site.

    200 000
   ________   x   6144  =  subtotal         = 11 592 452
     106  
    

2. Substitute the preceding value in the following calculation. This is the space for your current OCDS records.
3. Multiply subtotal by 1.5 to allow for additional OCDS growth.

       11 592 452   x   1.5   =  17 388 678 

4. Divide the total number of bytes per cylinder (using 3390 as an example) into the total number of bytes used by the OCDS. If the result is a fraction, round up to the next whole number. This number is the number of cylinders you should allocate for the OCDS data set.

   Total bytes used by the OCDS		(total = 17 388 678)
   __________________	=	__________________	=	23.6 or approximately 24 cylinders
   Total bytes per cylinder (3390)		737 280

If your installation has only active data (that is, no migrated data), see Estimating the number of data sets (mds) using DCOLLECT and Estimating the number of data sets (bver) using DCOLLECT for information about how to estimate the number of active data sets in your storage environment.

In the previous calculation, substitute the number of D type records for mds and bver.