Virtualise your servers

Posted on 19 Nov 2009 at 11:29

Jon Honeyball walks through the three steps to virtualising servers

All of these are excellent reasons for virtualising, but you need to know which one is for you. Once you know that, you can choose your destination host hardware platform.

If you have a rack (or a desktop box) filled with skipware then it’s a good idea to put some more modern hardware in place. I’d go for the latest hardware available from the vendor of your choice, as the price/performance ratio is always best on new hardware, as is the computing load per unit of power, noise and heat output.

It might feel like a good idea to press some redundant older hardware into service, but I’d advise against this. Spend the money on modern boxes.

The next question is “how many boxes do we need?”, and there are several different views on this. If your current servers are heavily loaded then you can probably go for a 4:1 ratio, squeezing four physical servers down onto a single virtualising host box.

It might feel like a good idea to press some redundant older hardware into service, but I’d advise against this. Spend the money on modern boxes

If your existing servers are only lightly loaded then that compression ratio could be considerably higher – I’ve seen 16:1 in a real-world deployment. I’ll admit that the 16 old servers taken out were low-performance items doing a set of relatively lightweight tasks, because their previous IT managers had followed a rather indulgent strategy of “a new server for each new task” on their network.

The result was a huge pile of tin, little of which was doing any real work. You’ll need to do a realistic evaluation of the loadings on your existing server hardware, and then make a guesstimate for the new boxes.

Of course, this is where experimentation can prove valuable – move some of the old machines over and do a trial setup.

Whatever configuration you end up with, there’s no such thing as too much RAM – it’s far more important than CPU power and even disk space where virtualisation is concerned. I’d rather have a box with two quad-core processors running at 2GHz than one quad-core running faster for the same money.

You also need to work out the real-world memory requirements for your servers and come to a view based on how many virtualised loads will be running on each box. But be realistic by starting from 16GB of RAM for each server (and think about going to 32GB).

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