vCenter Design: Why you should run it virtual …

Note: There can be still some use cases, where it makes sense to run a vCenter installation directly on a physical host. Like in all design considerations the only “correct” global answer is “It depends!” 🙂


A colleague asked me last week, if it wouldn´t be more secure to run vCenter beside the ESXi hosts on a separate physical host. His idea behind was, that if the whole vSphere environment would be down / unreachable you still have a physical server with running vCenter independent.
One of the first things you should be asking yourself when starting planning your vSphere design is “How important and critical is the whole environment to me?” and “How long can it be acceptable that the vCenter server is unreachable?”.
To give yourself an answer to this questions it`s necessary to know what features / services are effected when the vCenter server is down. Many people believe that all options / features you configure via vCenter are affected. That’s not true! One of the most important features without a doubt is HA. Even if you need vCenter to create clusters, where you can enable HA etc., it will work even if the vCenter server goes down. Of course there are many things more you should know, but that is not the scope of this article.


To get started I think it´s the best to comparing some possible “disaster”-events to your vCenter and the difference, if it´s running on a physical server or as a virtual machine.

Not really unlikely would be a hardware failure. If you are not using any failover software (like VMware Heartbeat) and your vCenter goes down, it doesn´t matter if physical or virtual in the first step. But if you running it as a VM it will take HA just a couple of seconds to notice the host-failure and all the affected VMs gets restarted (including the vCenter-VM in this example). The total downtime including booting and waiting for all services to come up should be < 5 minutes. I think everybody will agree, that it will take multiple times longer to fix a physical host (with the vCenter installation on it), doesn´t matter which hardware-failure need to be fixed (or the whole server replaced).

Let´s continue with a software failure (broken operation system / corrupt database, whatever…). To make this example more clear let´s assume that you lose all your data of your vCenter server and you need to recover everything from your backup. Here we have two interesting factors: a) How much time does the complete restore take? & b) How much effort / steps do you need to complete? Of course this depends very much on the backup product you use (either for physical or virtual server), but I guess most of you will agree that the whole backup-thing got much easier and faster in virtual environments instead of “the old days” without virtualization.

The next “category” would be server maintenance. It doesn´t matter what kind of maintenance you need to perform, you will always have a downtime, if your vCenter is running directly on the server which need to be maintained. Compared to a VM: A virtual vCenter benefits from all cluster features like vMotion for example, which will reduce the downtime to exactly 0. Also features like Hot Add can be used to upgrade your virtual server hardware without even a reboot!

Meantime also VMware recommends running vCenter as a virtual machine as a best practice.

A little bit different the whole thing can be, if a failover software like VMware vCenter Server Heartbeat (in the meantime there are also products from 3rd parties available) is used. Typically it´s only used in really critical environments or in big enterprise environments, where no one cares the additional license costs 🙂  You can find more information about this product on the VMware homepage: http://www.vmware.com/products/vcenter-server-heartbeat/overview.html

Like mentioned on the beginning on this posts; You always need to consider a vSphere design on its own!

Comments

  1. Great,
    Dell has provided very good documentation on how to make VCenter highly available
    http://www.dell.com/vmware
    http://www.dell.com/downloads/global/power/ps4q05-20050285-Stanford.pdf

  2. Ben Steinfeld says:

    It is actually a great and useful post!
    I am glad that you shared this helpful info with us. Please keep us up to date like this.
    Thanks for sharing.

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