While there are many tools to view or analyze the current server performance and behavior, how do we examine historical activity? Most Linux systems rotate logfiles in /var/log for varying periods of time. Unfortunately, these are programs and system logs, not performance measurements.
When we installed the sysstat package in a previous recipe, we gained the use of the sar utility. Some argue that sar is the Swiss Army knife of metric collection. A simple invocation can display past data regarding memory, CPUs, IRQs, disk devices, networks, or even TTYs.
When administering a highly available server, there are a few things as helpful as performance trends. Let's examine them.
As sar and iostat are both part of the sysstat package, we recommend that you review the Evaluating the current disk performance with iostat recipe before continuing.