I think the principal difference is how expiration of data is handled. Archives expire by time; backups expire by the number of versions stored. Consequently, which pool to use for the DB2 backups depends on how your backup and recovery policy is formulated: if you keep backups for a certain period of time they should be in the archive pool; if you keep a given number of backup generations they should be in the backup pool. Archived logs, despite their name, should be in the same pool with the backups as they are usually meaningless without the backup itself.