Hi Sergio, Some of the directives I found helpful for our MASTER server are listed below. Since status.dat and nagios.cmd are disk bound, put them on ramdisk will be faster. status_file=/mnt/ramdisk/status.dat command_file=/mnt/ramdisk/nagios.cmd I don't think aggressive_host_checking is needed as nagios checks for host when a service is in error anyway. use_aggressive_host_checking=0 check_host_freshness=0 Service freshness is important as the MASTER tends to process passive checks much slower so the services may go stale. However, since our checks are 5 min interval, having the MASTER wait for the next round of check is fine. check_service_freshness=1 service_freshness_check_interval=420 We use nagios-3.2.1 and I think these directives are still experimental but they seem to help. You will see defunct nagios processes that come and go. I think it's caused by child forked once instead of twice so one gets killed (my theory), but again, it seems to be running ok. use_large_installation_tweaks=0 child_processes_fork_twice=0 Our MASTER receives ~7000 passive checks from the SLAVE but it could only process max ~5000 passive checks per 5 min. The latency is about <10 secs. For the rest, the MASTER actively checks them. If you or someone knows a way to improve passive check processing, that will be great. Also, in our setup, we don't use NSCA. The slaves have ocsp_command=send_service_check where this command inserts the checks into a file that gets sent every 5 sec to the master. On the master, there's a script that opens this file and inserts the lines directly into the nagios.cmd pipe every 5 sec. Trisha