As the size of the Netflow database is primarily determined by the number of received flows and how long network data is kept, the NfArchive database's size is relative to your network environment and retention settings.
When this database grows large, there are two main factors for controlling database size. On the Flow Settings dialog (On the Flow Monitor section of the GO menu, select Configure > Setting), you can control how long data is kept in the Archive database by adjusting the Expire archive data after setting. By default this is set to 7 days. If your network policies dictate you keep data for longer periods, or your network environment is large enough, you may need to move to an edition of SQL that does not have the same space limitation as our default instance of SQL Server Express. For more information, see the WhatsUp Gold Database Migration and Management Guide on the WhatsUp Gold web site.