Q: Is each file matching to one DataNode?
A: No – data is partitioned by its expiration day. The expiration day is the day the record was collected plus the “days to keep data” as specified on the InfoNode\Data setup page (Log entries have expiration offsets as well).
Files are deleted to make room for new data when the database is full. This significantly improves purging performance of the 4.5.x database structure. It also allows for much more efficient archiving since older files become static. Differential backups are now possible (you only copy the files that have changed).