Time

A few months ago, I was helping out a customer with a time configuration issue on their vSphere environment. For one specific question, I investigated and wrote the post:

ESXi Time Configuration: Don’t point it towards the Windows Domain name

However, while doing the investigations, I went through various documents produced by VMware. As NTP (Network Time Protocol) configuration is something that is frequently done wrong, I thought I should gather the documents I went through in this quick blog post. That will not only benefit me but also other people having the useful links on one page.

First of all, if you have time, VMware has this excellent whitepaper titled: Timekeeping in VMware Virtual Machines  This document is truly a “Chapter and Verse” on timekeeping in vSphere environments. It also discusses the minor differences in the way timekeeping behaves, depending on hypervisor and/or guest OS installed. Also, have a look at the “Troubleshooting” section, for detailed information on how to get increased logging while troubleshooting etc. This is a document one must read in order to understand timekeeping in vSphere or at least, keep with oneself at all times.

To get a good NTP hierarchy, one must have good time sources. For Windows, things have changed over the years. To have them configured correctly, VMware has this knowledge-base article released, discussing best-practices for a Windows environment: Timekeeping best practices for Windows, including NTP  A very useful document to ensure configuration is correct, whether the machine is member of a domain or not.

Typically, people assume that disabling time synchronisation with host is enough for a VM to never synchronise time with it but there are certain cases when a virtual machines still synchronises time with the host. For example, when a virtual machine is resumed or reverted to a snapshot etc. For that reason, at times, you might want to disable time synchronisation completely. The whitepaper mentioned above discusses this subject in great detail but the knowledge-base article: Disabling Time Synchronization describes the process of implementing it.

Lastly, I wanted to mention this knowledge-base article: Troubleshooting NTP on ESX and ESXi 4.x / 5.x  Purpose of this document is pretty self-explanatory but a good thing about this document is that it discusses troubleshooting NTP for not just the current ESXi versions but also the classic ESX as it’s subtly different in some areas. Assuring to know that VMware still hasn’t forgotten the classic ESX.

Hope the links to these documents will aid people in understanding/troubleshooting NTP in vSphere environments. They will certainly be a good reminder to me!