In this recipe, we will get started by showing the tools that can be used to monitor the Input/Output (IO) from a block device. We will then show how to tune the way that the Linux Kernel handles IO to meet your requirements in the best possible manner and finally explain how the Kernel handles IO requests in a little bit more detail.
In this section, we will see how to monitor the IO characteristics of your system using commands that will come installed on a RedHat or CentOS system.
The first command for monitoring IO is a command used most often for other things and it is called top
. Running top
and pressing 1 to show per-CPU statistics will give you an idea of what your CPUs are doing. Most importantly, in this context, the wa
column shows what percentage of time the CPU is spending waiting for IO operations to be completed.
In systems that are very IO-bound, this I/O waiting figure can effectively be 100 percent, which means that the CPUs in the...