Explanation: FREQUENCY(days) is an optional parameter of VOLUME specifying the number of days required between backup versions of a data set. DFSMShsm does not back up the data set unless the specified number of days has elapsed since the last back up of the data set. For days, substitute a decimal number from 0 to 999. For example, if days is specified as 5, only those data sets that have not been backed up in the last five days are eligible for backup. When you specify 0, DFSMShsm backs up changed data sets no matter how recently they were backed up.
Defaults: If you do not specify the FREQUENCY parameter with the BACKVOL command or have not specified the FREQUENCY parameter with an ALTERDS command, the value for FREQUENCY previously specified on the SETSYS command or the DFSMShsm default for FREQUENCY is used.