CDC Guide for z/OS

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Calculating the Data Set Size

Use the following formulas to estimate the size of each active log data set in bytes and then convert that value to tracks and cylinders for space allocation:

Formula 1
. To estimate the active log data set size in bytes:

active log data set size in bytes = (average change record size in bytes
                                    x number of changes captured per hour
                                    x hours between archiving) 
                                      x (1 + overhead rate)

For the overhead rate, use 5-10 percent.

Formula 2
. To convert the active log data set size from bytes to tracks:

active log data set size in cylinders = active log data set size in tracks 
                                            / number of tracks per cylinder

Formula 3
. To convert the active log data set size from tracks to cylinders:

active log data set size in tracks = active log data set size in bytes
                                        / number of usable bytes per track

The number of tracks per cylinder and the number of usable bytes per track depend on the type of DASD you use.

The following table provides these values for 3390 and 3380 DASD devices:

Space Information	Model 3390	Model 3380
Tracks per cylinder	15	15
Usable bytes per track	49,152	40,960

This table applies only to the PowerExchange Logger and is based on the fact that the PowerExchange Logger writes 4 KB blocks.

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CDC Guide for z/OS

CDC Guide for z/OS

Calculating the Data Set Size

Calculating the Data Set Size