The last time I wrote about XenServer and XenApp, I focused on a whole set of items like manageability, availability, flexibility and utilization.  This time, I want to focus directly on utilization as based on the feedback I’ve received it seems it’s the one many people are interested in.

Even before the scalability numbers of XenApp and XenServer came out, I had numerous conversations about virtualizing XenApp.  And now that Citrix is showing the XenServer overhead for virtualizing XenApp, those conversations have increased, but I think some critical points are being lost.  A couple of months ago, Citrix did scalability tests to identify that XenServer has roughly a 7-8% overhead when virtualizing 64-bit XenApp, and roughly 20% when virtualizing 32bit XenApp servers.  I was like WOW, 64bit is great, barely any overhead.  But how many people are actually running a truly 64bit environment?

Most people have the hardware, as it has been sold for years. Most people also have access to the 64bit version of Windows and XenApp. So why aren’t we all jumping on the 64bit bandwagon? Because it’s the applications. Unfortunately, many applications that XenApp environments run are 32bit, and some are still 16bit!  This conversion to 64bit applications will take time (Does anyone else remember the 16bit versus 32bit migration that happened years ago? It wasn’t an overnight thing. It took time. And yet there are still 16bit apps out there.)  So this fact makes it highly unlikely that organizations will be able to convert their XenApp environments into complete 64bit setup. This means many will stay with 32bit only or else have mixed 32/64 bit environments.  So let’s focus on the 32bit environments, are they virtualization candidates?

Maybe And most likely Yes.

Take a look at many XenApp deployments and what resource do you typically exhaust first?  RAM.  It is because in Windows 2003, we are limited to 4GB of addressable RAM.  So, when we hit that limit, everything else in the system is wasted (processor, IO and networking).  And I’ve seen some applications take enormous amounts of RAM. Just the other day I was working on some detailed Visio drawings and Visio took 1GB of RAM.  Yes, I said gigabyte.  (Of course the drawing was about the Simpsons and how Homer stays at the forefront of technology – He even had a blog called “Mr X. – All the Muck That’s Fit To Rake”).  So, a 20% overhead on 32bit systems? I probably wouldn’t notice as my entire server is barely utilized except the RAM.  

RAM is easy to install and one of the cheapest things to add to a server.  Use the same hardware and increase the RAM to at least 8GB.  Now, try to run 2 virtual XenApp servers.  You might not double your user concurrency, but you will get pretty close, which will equate to hardware and power savings.

So take a look at your physical XenApp servers. Is the RAM fully utilized? What about the processor utilization levels?  I bet more likely than not the RAM is fully committed and the processors are running at 10-40% utilization. 


(Homer Simpson Quote: “I want to share something with you: The three little sentences that will get you through life. Number 1: Cover for me. Number 2: Oh, good idea, Boss! Number 3: It was like that when I got here.”)