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Dan Feller on my team contributed at least two posts on the topic of virtualizing XenApp servers on XenServer. Dan makes some excellent points and gives you plenty of business reasons why XA on XS is a good idea.
I am not going to re-iterate Dan's points here, but rather focus on another burning question in this context: How much of a scalability overhead can I really expect with my specific application? The typical consulting answer would be "it depends" and "we'll have to do a scalability / performance assessment to determine the specifics and best practices". So, we have done just that and used two popular enterprise class Applications: Siebel 8.0 and PeopleSoft 9.0. The Solution Center is one of the teams under the umbrella of Worldwide Consulting Solutions (Dan Feller's Integrated Solutions team is another) and focuses on these types of projects, which often involve third party applications and/or hardware platforms from our technology partners.
Recently, we looked at running the front-end of Oracle's PeopleSoft and Siebel applications on XenApp (both 32-bit and 64-bit platforms) and focused on comparing the user densities we could achieve on "bare metal" servers compared to running them on XenServer.
The results are published in two separate whitepapers (PeopleSoft, Siebel), which describe the test bed, test methodology, detailed results and interpretation. As Dan stated in his May 15th posting, the virtualization overhead can be as low as 6% for XenApp virtualization on XenServer, and our tests confirm this number. Of course, the numbers vary between the applications and platforms, and we describe all the details in the whitepapers.
Generally speaking, kernel memory limitations constitute the first bottleneck on 32-bit platforms, and our tests verified that behavior. Even with the popular /PAE switch, the kernel memory limitation remains at 2 GB. Therefore, you can expect a higher user density per physical server if you're running multiple 32-bit XenApp servers on a XenServer. You'd have to be cautious not to consume too many CPU cycles, which often become the next bottleneck once memory is no longer a major concern. Prices of multi-core, multi socket servers with plenty of RAM have come down significantly, so chances are that your latest servers have plenty of resources to run reliably in that configuration at a reasonable price:
According to this 1988 article, prices of 1 MB memory chips were as high as $60 (or $105 in today's money), while you can buy a barebones server with 64 GB of RAM for roughly $5,000 today. While I am on the topic of computer nostalgia: a 150 MB hard drive set you back over $8k in today's dollars way back when... 1988 was also the year Dan Feller was looking forward to seeing his favorite TV show getting its own slot in the line up and he is still enjoying it to this day, as you can see from the quotes in his postings on this site. But I am digressing...
The Solution Center also conducted detailed validation tests with Oracle to obtain validation status for running virtual images of the Web-, Application-, and Database servers of Siebel 8.0 , PeopleSoft 9.0, and Oracle E-Business Suite 12 on XenServer 4.1, so you can now be confident that the entire environment can be successfully virtualized on XenServer, allowing you to take advantage of XenMotion in case of hardware failure and other benefits.
Citrix XenApp Platinum Reference Design is an independent publication originally created by Rick Dehlinger the CEO/Chief Technologist of the iQurious Corporation in 2004 / 2005. From 2005 through 2008 Roddy Rodstein maintained and re-distributed the publication.
I'm honored to have both these brilliant minds as close friends of mine.
If you don't know Rick, you're probably new to this industry or have been kept far away from all technical conversations around Citrix. Rick is one of Citrix's Technology Professionals - a true community leader and CEO of a Citrix partner company named iQurious where he applies his revolutionary technical vision around App Delivery.
Roddy Rodstein is a world-class technical guru for Citrix products, he's been the most active and renowned SEs in the community while working for Citrix; Roddy recently started his own company named SE Outsourcing.
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This Paper is a complete guide covering every aspect of XenApp Platinum; If you have Citrix XenApp currently implemented or you're thinking of delivering your applications using XenApp technology this is a must read!
Fantastic Job Guys, you know I'm a big fan! 
To download the whitepaper visit: http://seoutsourcing.com/node/28
Cheers,
Gus Pinto
Twitter/GusPinto
The following Citrix virtualization white paper discusses how Citrix XenServer provides simple, economical server virtualization designed for easy implementation in any IT environment. From the simplicity of "10 Minutes to Xen" installation to a full range of complementary, best-of-breed solutions from independent solution providers, Citrix XenServer offers innovative, cost-effective solutions for application availability, business continuity, rapid provisioning, and end-to-end visibility and management across virtual and physical environments.
Adoption of virtualization is concentrated among large enterprises, while adoption by mid-sized companies has been much slower. For these companies, enterprise-focused virtualization solutions often present barriers including:
- fragmentation between new, virtualization-ready operating systems and legacy platforms running mission-critical applications
- application performance constrained by storage and network I/O on virtualized servers
- server and storage constraints imposed by virtualization platform providers
- security and resiliency concerns raised when multiple critical applications run on the same hardware
- implementation hurdles created by complex interdependencies and demanding installation protocols
- vendor lock-in issues, raising pricing and support risks many companies prefer to avoid
- application delivery constraints imposed at virtual/physical boundaries
Download the white paper here: Virtualization Everywhere
Learn hands down how to implement Citrix XenApp with NetScaler.
Here's a paper that can show you how.
This whitepaper discusses Desktop Virtualization and the impact on desktop management challenges.
- The challenges for desktop management in a pre-Desktop Virtualization world.
- How these challenges are addressed by Desktop Virtualization
- Issues that are not well addressed by Desktop Virtualization
- Our view of how to best address these remaining issues.
Enjoy the reading!
Gus Pinto
This white paper will discuss how customers can achieve faster deployment, higher reliability, easier management, and reduced server foot print by virtualizing Citrix XenApp using XenServer.
You can also listen to the postcast around this subject:
cheers,
Gus