Nov 09
Memory sharing – VMware has it and the others don’t! (Part 2)
Eric Inch
I enjoy learning, using and helping others through technology. This is my second year with C/D/H after many years of consulting for numerous small and mid-sized companies. I enjoy challenging projects and continual improvement in all areas. Most recently, I have been working to help grow the virtualization practice at C/D/H and hopefully add that area to the already impressive expertise in infrastructure consulting at C/D/H.
When I’m not working, I enjoy spending time with my family. I have two little girls who keep me extremely busy but are always the highlight of my day.
For a more in-depth bio and a list of my areas of expertise, please visit http://www.cdh.com.
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Articles by Eric Inch
In a previous post I discussed an advanced feature that is included in only one of the leading virtualization platforms and involves the ability to over commit memory. I am, of course, talking about VMware’s unique ability to overcommit memory through a technique known as transparent memory page sharing. In this posting, which I will so cleverly call “Part 2”, I will discuss another technique used in overcommitting memory, the balloon driver.
The balloon driver is added to the guest OS as part of the VMware tools installation. The driver works with the server to reclaim pages that are considered least valuable by the guest. It essentially acts like a native program in the operating system that requires more and more memory in a predictable manner. The balloon driver continuously puts a stress on the OS to cover the desired amount of memory to be used by others. This can be thought of as the inflation of the balloon. The balloon driver technique effectively increases or decreases memory pressure on the guest operating system, causing the guest to invoke its own memory management algorithms. When memory is tight, the guest operating system decides which pages to reclaim and will swap them to its own virtual disk if it deems necessary.
I think this technique for overcommitting memory is extremely valuable as it addresses one of the main reasons for choosing virtualization in the first place, to gain better efficiency of your underutilized servers. VMware’s competitors that lack this functionality aren’t really providing the necessary features required to maximize efficiency of resources. Why not choose a virtualization solution that extends memory management capabilities to sharing resources between guests? VMware is the recognized market leader; memory overcommit is a competitive advantage and an example of a feature that will allow them to maintain a stronghold on enterprise environments for the foreseeable future.