When Was the Last Time you VMotion-ed?

I have a consulting client with a relatively small vSphere implementation.  Comprised of just four ESX servers, this client typifies the small implementation.

Yet while small, they’ve been smart in how they’ve constructed that virtual infrastructure.  Their ESX servers connect to a central SAN, enjoying all the VMotion benefits that working off a shared Datastore brings.

I was taking a look at their configuration a few weeks ago when I noticed that their configuration didn’t include creating a cluster.  Each of their hosts was displayed individually in the vSphere Client, showing their virtual machines by host rather than as part of a larger resource pool.

I asked this client, “Wouldn’t you want to create a cluster out of these hosts, so that you can share the resources between them?”

Their response was one I wasn’t expecting, “Well, we thought about that.  But we found that we really don’t use VMotion pretty much ever.  We know that we can use VMotion, and sometimes we do.  But, our performance is acceptable so we don’t need DRS, and we find that that we’re really never doing activities that require us to relocate or re-balance our virtual machines.”

That response really got me thinking about the uses of VMotion in contrast with all the publicity its feature gets in the IT press:

  • You use VMotion prior to rebooting a host.
  • You use VMotion to re-balance load (often through DRS’s automated processes)
  • You use HA after an unexpected failure.

Each of these three use cases are important, but at the same time they don’t occur all that often.  ESX’s Linux roots mean that host reboots are a rarity.  Loads indeed need to be re-balanced, but this client (and others which I asked after having this conversation) doesn’t see the need to add its extra complexity.  HA indeed protects hosts after a failure, but other than the occasional full power outage hosts don’t tend to fail too often.

This brings me to this post’s question:  When was the last time you VMotion-ed?  Was it recently?  Do you do it often?  Or, now that your virtual infrastructure is up and running in steady-state, do you find that you really don’t use it all that often?  Give me the low-down in the comment field below.

Discuss this Blog Entry 10

jlchannel (not verified)
on Jun 17, 2010
Your customer should only buy Essential version. hehe.....
john (not verified)
on Sep 18, 2010
We have a vSphere implementation similar to the one you described. The only difference is we have configured HA, DRS, FT.

Ultimately, it is about my quality of life. Call me selfish, but after a long day, the last thing I need is a phone call at 1:00am about several VM's going offline because we had an ESXi host failure. Yes, this may be a rare event but we all know it only has to happen once.

Hstagner (not verified)
on Jun 17, 2010
Just a few small points to clarify for those new to VMware that may be reading this.

First, VMotion and HA are two different things. You don't use "VMotion's HA".

HA or High Availability is when you have a host failure (for unplanned downtime).

VMotion is a live migration (for planned downtime such as maintenance). I find that those new to VMware get these two confused all the time.

DRS (Distributed Resource Scheduler), not DRM (Digital Rights Management?) is a feature that VMware uses to balance the load across the cluster of available host resources utilizing the VMotion functionality.

Having cleared up those few items, here is my perspective.

My clients like being able to use VMotion to do maintenance during normal business hours on their hosts. I see it all the time.

My clients also enjoy not worrying about performance at the host level (like you would do in the physical world) by utilizing DRS. As long as they have enough resources in the cluster and their virtual infrastructure architecture is properly designed, they don't have to worry about manually placing or load balancing their VM's on certain hosts.

StevePantol (not verified)
on Jun 18, 2010
A friend in a shop sized similarly to the one you've described recently asked me about the same question--was vMotion worth it, given the cost, and how often did we really use it. I added it up cluster by cluster in the vSphere Client--over 9,000 times over the last three years.

So, yeah, we use it pretty often. Many of these are related to updates--going from 3.0 to 3.5 to 4, plus the Update packs in between. But we do see a trickle of daily DRS-related vMotions, too.

Hstagner (not verified)
on Jun 18, 2010

To clear up any confusion, I believe that jacob b is referring to the fact that the ESX Service Console is based on Linux. However, the hypervisor kernel itself is VMware (not based on Linux at all). ESXi actually does not have the service console and has nothing to do with Linux other than the lightweight busybox environment (shell). But now that's splitting hairs.

This is a common misconception and it is important to know this distinction. That being said, it is always better to explain this distinction rather than just saying "You're wrong..."

Upwind7 (not verified)
on Jun 20, 2010
He he he ... ESX based on Linux ... good one :) :)

Service Console in based on Linux, but not the hypervisor kernel.

on Jun 18, 2010
@Harley: Thanks for catching me on a couple of typos! I've fixed them in the text.
jacob b (not verified)
on Jun 18, 2010
Since when was ESX Linux-based? You should probably learn more about the technology you are blogging about...
OldChewie (not verified)
on Jun 18, 2010
Jacob, have you never rebooted an ESX server? Or pressed Alt-F1 to access the console? It is COMPLETELY Linux based. Why else would I use a Putty session to manage the host?

I think you need to go back and modify or delete your comment.

YOUR ignorance is showing.


James (not verified)
on Jun 18, 2010
Great article Greg. I always ask the business, "how important are these virtual servers to you?". If it is worth the cost to your business to have HA, then get it. Don't just get it cause it's a neat-o thing to do.

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