Try using Netdata to monitor your server. It gives you a better view into what is happening. Recently I reduced the load a backup placed on the server by configuring it and monitoring it's real time load.
It give a lot more info than just knowing CPU and Mem stats. As it alerts for several sane things by default and allows you to see how each subsystem is performing. Really impressive and easy to intergrate.
I recall a release announcement saying Directadmin is also created intergration for Netdata.