Part 2: How People use VMware with Citrix Today
Today, VMware offers two core server products: ESX Server and GSX Server. Both are similar in function. GSX Server installs as an application and runs in an existing (Windows or Linux) environment. Similar to VMware Workstation or Microsoft's Virtual PC, it allows you to run multiple virtual machines. However, since GSX runs on an existing platform, rebooting the host operating system means you have to temporarily take down the virtual servers.
ESX Server is VMware's flagship product. Instead of running on a host operating system, ESX Server runs on a tiny Linux-based rock-solid microkernel. Individual virtual servers can each be brought up and down, independent of all others. VMware also offers an SMP option for ESX Server, so you can tie multiple physical processors to a single virtual server. For example, you could use ESX Server to run eight dual-processor virtual servers on a single sixteen-processor box.
In addition to simplified management and instant server provisioning, one of the real advantages to using virtual server technology today is the economies of scale that can be realized with resource sharing. (Of course this is something that every Citrix administrator understands well.) When using VMware, virtual machines can “share” memory, CPU, disk, and network capacity with one another.
So, for your Citrix or Terminal Server environment, should you consider building a few large VMware servers instead of building many smaller servers?
The most important thing to consider when answering this question is that a VMware virtual server should be thought of no differently than a standard physical server. All of your server design elements—user load, application load, application management, dealing with rogue applications—are 100% as relevant in virtual server environments as they are in standard server environments.
You first need to design your server and application strategy (as outlined in my new book, for example). Only then would you make the decision as to whether you deploy physical or virtual servers.
The popularity of VMware is without a doubt increasing. But is anyone actually using it for Citrix or Terminal Server environments? Last week, I spoke with Michael Mullany, VMware's Vice President of Marketing. He told me that there were really three areas where VMware is actively used in Citrix and Terminal Server environments.
The first is in environments with specific applications that are kernel-memory bound. Due to the kernel memory space limitations of Windows (discussed in Part 1 of this article), some applications cannot support more than ten or so users per server. By virtualizing the servers, companies can greatly increase user capacity per physical server and decrease server counts. (Conseco is one company who has very publicly acknowledged that they use VMware and Citrix for this purpose.)
Another specific use of VMware in Citrix environments is when companies have standardized on large Intel servers. The folks who run some companies like the idea of VMware so much that they've decided that all their servers in all their datacenters will run VMware. In these cases, obviously, companies run the Citrix servers in VMware environments.
The third use of VMware for Citrix is perhaps the most compelling, and it's when companies require rock-solid, 100% uptime environments. If you've thought it's impossible to transfer a running ICA session from one physical server to another—think again. You can do this with VMware!
This is done via an add-on product called VirtualCenter. VMware's VirtualCenter product allows you to virtualize your entire datacenter. VMotion technology actually allows you to transfer a fully running, live, and active virtual server from one physical server to another. With VMotion technology, you can run a Citrix MetaFrame farm where you never have to cut off users' sessions for maintenance. Ever.
As cool as that is, however, it's much more than most people require in Citrix and Terminal Server environments. For the most part, server-based computing environments will continue to be designed with build-out strategies. In most cases, the added cost of VMware does not product the ROI required since you can often fit more users on built-out blades or 1U servers.
On the other hand, if your organization falls into one of the three categories listed above, you'll be happy to know that Citrix runs very well in VMware environments, with full vendor support.
Check back Friday for the final part of this article. Part 3 will discuss the future of VMware and Citrix. How will EMC's announced intentions to buy VMware affect things? What about Microsoft's upcoming release of their Virtual Server product?