esxtop Demystified Part 1

      Vmware provides a tool called esxtop to monitor the performance of vSphere esxi hosts. This tool is capable of monitoring all aspects of an esxi host like cpu, memory, disk, network i/o. The problem is when a new vmware administrator runs the program for the first time it looks a bit intimidating. Lets tackle that problem by discussing what some of the information on the screen means.

When you first run the program you will be in the cpu view. This particular view will give you stats on the various processes that are currently running on your system. Along the top of the screen you will see things like uptime, the number of worlds, VM's, vCPUs, and CPU load average.

However if you are interested in other statistics you need to know the commands necessary to get to those screens. Pressing the "h" key will display the help menu. This menu will give you a list of all the available Interactive commands available.

Lets say we want to access network stats. All we would do is press the "n" key on the home screen and it would display each of your portgroups and the statistics related to it. You can try a few of the other switch displays to get a fell for switching between the screens.

Lets go back to the cpu view and discuss a few of the columns.

Below are the definitions for each of the columns on the default esxtop screen.

• ID -  Unique world ID. A world is an ESXi VMkernel schedulable entity, similar to a process or thread in other operating systems.
• GID - Resource group world id.  If you press e in esxtop and enter the number of the GID, this GID will expand itself to show all processes in that group.
• Name - Name of the world or resource pool
• NWLD - The number of worlds in the group, when this number is greater than one the row can be expanded to get more information on each world.
• %USED - Percentage of CPU that is used by that world or group
• %RUN - When this value is near the number of vCPUS X 100%, it means that all vCPUs in the VM are busy. 
• %SYS - percentage of time spent by system services on behalf of the world.
• %WAIT - Represents the percentage of time the VM was waiting for some VMKernel activity to complete such as I/O before it can continue.
• %VMWAIT -
• %RDY - Percentage of time that the VM is ready to execute commands, but has not yet been scheduled for CPU time due to contention with other VM's
• %IDLE - percentage of time the vCPU world is in idle loop
• %OVRLP - percentage of time spent by system services on behalf of other worlds.
• %CSTP - Percentage of time that the VM is ready to execute commands but that it is waiting for the availability of multiple VPUs as the VM is configured to use multiple vCPUs.
• %MLMTD - Percentage of time the world was ready to run but deliberately wasn't scheduled because that would violate the explicit CPU limit settings. 
• %SWPWT - Percentage of time the world is waiting for ESX VMKernel swapping memory. If this is high it means the VM is swapping memory.

This should be a great intro into the basics of using esxtop. Look forward to Part 2 coming soon.