What Kind Of Servers Should I Buy for VMware?

Another frequently asked question: What kind of servers should I buy to start my VMware cluster out?

My off-the-cuff answer: “the biggest machines you can afford at least three of, from whatever vendor you like the most,” followed by “it depends.”

Part of the great thing about virtualization, especially with VMware, is that you can use VMotion to move everything off of a running machine. This means that you need a place to put that workload, though (think of my “buckets of water” analogy). If you buy two machines you have to keep one empty, and 50% of your cluster capacity sits idle. If you buy three machines you can use two of them, and 33% of your cluster capacity sits idle. Four machines, 25%.

Of course, you don’t want to buy machines smaller than the workload you’re going to virtualize. If you want to virtualize an application that will need 8 vCPUs you want to consider carefully whether you’d want to purchase 8-core servers or go for something like a 16-core machine.

CPU isn’t the only consideration. You need to think about RAM sizing, too. Do you get three machines with 256 GB of RAM each or seven with 96 GB of RAM? What’s the sweet spot for pricing, versus the size of your largest VM? What does it cost for each new server you put in, in incremental costs, like KVM, SAN, and network switch ports? That should play into this, too, because those things aren’t free, and they contribute to the cost of the environment. Would you rather spend $3000 on infrastructure costs or put that $3000 into the machines?

As you see, and as with many things in IT, there’s no “best way” to do things. It’s all about you, your workloads, and your budget.


This is the third post in my series of “what VMware questions do I hear most often?” The first two questions were:

  1. How much capacity should I have for VMware?
  2. Should I convert my old servers to ESX?

If you think of a question you’d like me to answer please put it in the comments. Thanks!

4 thoughts on “What Kind Of Servers Should I Buy for VMware?”

  1. A big consideration when sizing your servers is the scale-out vs the scale-up debate.
    Scale up has the pro of consolidating more vm’s onto fewer hosts thus saving space and power (and some savings in mgmt). You can easily get 60+ average vm’s on a host with 16 cores and 64 GB ram.
    I prefer a more scaled out approach, limit the number of vm’s per host to less than 20. This gives you more flexibility and less waste on the n+1 redundancy. Ex 8 cores 16-32GB ram.
    A big thing for me is being able to quickly migrate all vm’s off a host for maintenance, cluster rebalancing etc etc. with smaller hosts, and the right setup, you should be able to accomplish this in less than 10 mins, large hosts can take hours.
    As for hardware, I’ve used Dell and HP and haven’t had any problems with either, just make sure you get all your servers as identical as possible and talk to the vendor about future compatability esp re vmotion (check out vmware EVC for more details).

  2. I like the idea of keeping the three boxes slightly underutilized so that when you need to empty that third box, you can fit it into the other two. This job gets tougher once you have resource reservations and limiting in the picture.

    VMware’s page sharing helps a little bit, with respect to RAM utilization. RAM is usually the biggest limiter in these considerations.

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