If the Server batch type field is set to 'Batch archiving by days', use the Older than field to enter how old the data must be before they can be archived, for example 'Older than 365 days'.
If the Server batch type field is set to 'Batch archiving by date', use the Older than field to enter a reference date. All data older than this date, for instance 'January 01, 2011', must be archived.