How To - Linux Server Performance

It is important to have a basic understanding of how to check out your Linux server's performance to help diagnose / troubleshoot various issues. Below is some useful tools and reference materials I have found helpful.

iostat - disk utilization
This article is a good simple reference on using IOSTAT.
top - cpu utilization
"The top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel.
ifstat - network interface utilization
Extremely handy tool to see if you are saturating your network interfaces. eg, in an NAS environment this could be very useful.
20 Linux System Monitoring Tools Every SysAdmin Should Know