Marathon Technologies released a couple of whitepapers and a blueprint for optimizing Citrix XenApp High Availability. As you know, the technology for HA in Xenserver is actually from Marathon and you can also enable Fault tolerance with Marathon EverRun VM. These documents aren’t about Xenserver, but “a set of planning and implementation tools designed to help companies ensure high availability of applications delivered with Citrix® XenApp™ more efficiently and cost effectively“.

The documents are a good read if you want to learn more about XenApp and about how you can protect each component of XenApp.