CA-IDMS stores database area status information in its system journal files, in what are known as journal header records. By default, there are three such records in each system journal.
In a large CV with many database areas, this may not be enough.
The MAX AREA parameter on the FORMAT JOURNAL statement will cause the FORMAT utility to generate enough JHDA records in the system journals to allow them to hold the information for the specified number of database areas.
Ultimately, the journals will be able to hold more area entries than what is specified in the MAX AREA parameter because it will allocate the number of JHDAs necessary, and then the CV will actually use all of the space in the JHDAs.
For example, if the journal block size is 2004, then each JHDA can hold (2004 – 32) / 8 = 246 area entries.
If MAX AREA = 2953 is specified, 13 JHDAs will be needed to hold that many, but they will actually be able to hold 13 * 246 = 3198 area entries.
By taking the “max of” amount in the DC205031 message, adding one, and using that for the MAX AREA parameter, you are adding one more JHDA block to the journals.
https://docops.ca.com/ca-idms-ref/19/en/utilities/utility-statements/format#FORMAT-Usage (scroll down to "When to use MAX AREA").