Place a checkpoint statement in your slapd.conf and remove the db_checkpoint command from your cron job. It’s better to let the application using the db (slapd) do its own checkpointing.
Continue to run db_archive from your cron job to identify unneeded log files. Either delete them or archive them to tape as desired.
You should also upgrade to the latest stable version of OpenLDAP. 2.1.12 is pretty old and a lot has been fixed since then. Remember, too that there’s one patch for Berkeley DB that needs to be applied.
Hope this helps,
Packaged, certified, and supported LDAP software: http://www.symas.net/download