The value n is the maximum size of the journal file, in megabytes. When a journal file grows to this size it will be closed and a new journal file will be created. For more information about journal file rollover, see the Caché Data Integrity Guide.
0–4079. A number of megabytes. A value of 0 (the default) means use the system default (currently 1024).
On the page System Administration > Configuration > System Configuration > Journal Settings, in the Start new journal file every... (MB) row, enter a number of megabytes.