Although VMware hosts are normally reliable, things can and sometimes do go wrong. When this happens, it is important to have troubleshooting tools that can help you quickly resolve the issue. One especially helpful tool is VMware’s Esxtop. This article runs down how to use Esxtop to pinpoint performance issues quickly.
Esxtop is a command-line tool that is natively included on your VMware hosts. To get started, connect an SSH session to the host server that you wish to examine. PuTTY works well for this purpose, but there are other tools available as well.
Once you have logged in, the first thing that you will need to do is to retrieve the VMIDs for your virtual machines. The Esxtop utility identifies VMs by their VMID, so creating a list of VMIDs ahead of time will help you to better understand the information that is provided to you. The easiest way to retrieve the VMIDs is to use this command:
You can see what this looks like here:
The first column displays the VMIDs of the virtual machines on this host.
Now, enter the Esxtop command to access the Esxtop interface shown here:
This is the information that is displayed when you enter the ESXTOP command.
As you can see in the screen above, the Esxtop tool provides a wealth of information about the host’s workload. Although this information might initially seem to be somewhat convoluted, it can be used to help track down performance issues.
The very first line of the display shown above provides information about your VM’s CPU usage. You will notice that this line concludes with a statement of CPU load averages, followed by three numbers (0.01, 0.05, and 0.15). The first number displays the load average for the last five seconds. The remaining numbers display load averages for longer periods of time (one minute, five minutes, and fifteen minutes).
The load averages should ideally be around 1.00. Lower values mean that the CPUs are being underutilized, while higher values mean that the CPUs are being overutilized. If the load average reaches 2.00, it means that the CPUs are seriously overloaded and that you need to either upgrade your host’s hardware or move some VMs to another host.
The VMware host displayed above is a lab machine with very low CPU usage, but if the load averages had been excessively high then the next logical question is which VMs are consuming the most CPU resources.
The easiest way to determine which VMs are currently using the most CPU resources is to look at the %Used column. This column reflects the percentage of the host’s physical CPU resources that a virtual CPU is using. Looking at the %Ready column can also be telling. This column reflects the percentage of time when the VPU was waiting to execute an instruction but had to wait for CPU resources to be made available. Ideally, the %Ready column should never exceed 5%.
The Esxtop tool is able to display resource usage data for more than just CPU resources. If you press the H key, you will be taken to a help menu that lists the various commands that are supported by the Esxtop tool. If you look at the bottom of the next screengrab, you can see a section labeled Switch Displays. The commands shown in this section can be used to look at other types of performance metrics. For example, pressing M displays memory data. Similarly, pressing N displays networking data.
The help menu lists the Esxtop tool’s various modes.
Press M to access the host’s memory metrics. This screen shows you the current virtual machine memory size (MEMSZ), as well as how much memory has been granted to each VM (Grant). You can also see how much swap memory is currently being used (SWCUR), as shown below:
The Esxtop tool provides memory usage statistics.
The main things to check for on the memory display are memory depletion and excessive swapping. While some swapping can be expected on a heavily loaded host, excessive swapping indicates that the host doesn’t have enough memory, and can also lead to performance problems. In this type of situation, you should add more memory to the host or migrate some of the VMs to another host.
Getting More Data
Finally, one of the most important things to know about using the Esxtop tool is that the displays are highly customizable. Simply press the F key and you will see a list of columns that Esxtop can display for the current mode. The next screengrab, for example, shows the columns that are available for the tool’s memory mode. The columns with an asterisk next to them are currently enabled, while the others are disabled. To display a column, simply press the corresponding letter. You can also press the letter associated with a column if you want to stop displaying that column.
Esxtop allows you to toggle columns on and off.
In a world filled with dashboards and UI, sometimes all you need is a command-line tool that provides you instantly with the details you need. Esxtop provides those managing VMware hosts with access to valuable and often insightful information that can be used to help make critical decisions.
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