Explanation

RETAINDAYS is an optional parameter specifying a number of days to retain a specific backup copy of a data set. If you specify RETAINDAYS, number of retain days is a required parameter that specifies a minimum number of days (0–50000) that DFSMShsm retains the backup copy. If you specify 99999, the data set backup version never expires. Start of change

Any value given on the command line greater than 50000 (and other than 99999) causes a failure with an ARC1605I error message. When a value is specified via the ARCBDEXT, any value greater than 50000 is changed to 50000. A decimal value of 99999 indicates that the backup copy should never expire. Any value less than 0 is changed to 0. End of change

A retain days value of 0 indicates that:

the backup version might expire within the same day that it was created if EXPIREBV processing takes place,
the backup version is kept as an active copy before roll-off occurs,
The backup version is not managed as a retained copy.