I have a nagios server running Ubuntu with a 2.0 GHz Intel Processor, a RAID10 array, and 400 MB of RAM. It monitors a total of 42 services across 8 hosts, most of which are checked using the check_http plugin even 5 minutes, some every minute. Recently the load on the nagios server has been above 4, often as high as 6. The server also runs cacti, gathering statistics every minute for 6 hosts.

I wonder, how many services should hardware like this be able to handle? Is the load so high because I am pushing the limits of the hardware, or should this hardware be able to handle 42 service checks plus cacti? If the hardware is inadequate, should I look to add more RAM, more cores, or faster cores? What hardware / service checks are others running?