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The VM World: It's all about IO

Friday, May 13, 2011 in Technical Articles (Views: 1973)
One thing that comes to mind when running VMs is how slow they can process, when multiple VMs are running. But, why is this, when you have plenty of memory, plenty of resources, and one fast host machine?

Simple, it's all about IO. In this article, I will go through and document a few of the tricks that I have found to increase your performance on Virtual Machines in general.

This isn't really specific to VMWare, Hyper-V, or VirtualPC, just general things to look out for.

1. Don't skimp on host hardware
This seems to be a given, but you do get what you pay for. If you want to run 4 server class VMs, and maybe a workstation or two, don't think 8GB will be enough. You are really cheating yourself. Make sure to have plenty with room to spare.

2. Don't skimp on the guests, either
I used to say that the best way to fix a memory leak was to limit the resources available to it. This is why in my day I ran Exchange 2007 with 1GB of RAM on Windows Server 2003, since store.exe was going absolutely crazy for memory. Simply put, if you don't have the hardware, don't implement this.

3. Stay away from dynamic disks at all costs
This option will save you disk space, but will cost you in disk IO every time the disk has to expand. It's better to allocate the disk space you need, and then keep it static. If you must, expand it manually later.

4. It's all about disk IO
Under the hood, you have a host OS - guest OS - and all of these resources are fighting for system IO. Building on point 2, give your guests plenty of memory, and then disable the page file on the guest OS. This is one way to speed things up. Also, if you have disk intensive apps running in VMs like SCCM, then move them to a different disk. This would also increase your performance, and made a world of difference for me.

One other thing I also did for OS deployment is disabled the pagefile right from the Task Sequence. The WMIC tool is a great command line way to do this.

5. If possible, don't use your host for other services/activities
This is where I am a semi-hypocrite, since I do a lot of my labs and testing right on my own laptop. But, if possible, try to avoid this.

Just a few things that I found that made life much better in the VM world. Hopefully this will be of some use to you as well.


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