Today many organizations who use XenApp are still bound to x86 platforms because of legacy applications which don’t run on a x64 platform. Sometimes an application does run on a x64 platform but is not supported by the vendor on a x64 platform. By sticking to the x86 platform, modern server hardware can’t be fully utilized due to the memory limit of 4 GB of the x86 platform.
To overcome this limitation virtualization comes to practice! Virtualizing a XenApp server has always been a challenge. However with the maturity of vSphere and current CPU’s, there isn’t a limitation anymore to not virtualize a XenApp server. In this article I will share you my experience of implementing a virtualized XenApp production environment for a customers and give you my recommendations for a successful virtualization of XenApp.
This article is split in different parts. In the first part I focus on the configuration of the XenApp VM. In the second part I will look at the application landscape and the underlying ESX host and in the last part I will look at the performance results.
Building a XenApp VM
The configuration of a XenApp VM is crucial to the performance of a virtualized XenApp server and has a direct link with the hardware configuration of the underlying ESX host. As with every VM there are four main performance aspects that need to be optimized for the corresponding workload: cpu, memory, disk I/O and network I/O.
CPU
The most important resource for the XenApp VM is CPU. XenApp VM’s tend to use a lot of CPU resources and this is most likely to be the first bottleneck. In creating you XenApp VM, there are two scenario’s: scale-out or scale-up. In the scale-out scenario there a lot of light XenApp VM’s created with one vCPU. In the scale-up scenario less VM’s are created with two vCPU. The main objective is to not over commit your physical CPU’s. Let’s say you have a ESX host with two Quadcore CPU’s, which is a total of 8 cores. If you create eight 1 vCPU VM’s, each VM can schedule a dedicated CPU. The same applies for 2 vCPU VM’s, if you create four 2 vCPU VM’s, each VM can schedule a dedicated set of CPU’s.
Depending of the workload on your XenApp VM, one of this scenario’s fits best. If you have light workloads the scale-out scenario might be best, but in most situations the scale-up scenario does the best job. In most circumstances, using 2 vCPU’s allows for more users and a more consistent user experience. With the improvements made to the CPU scheduler in vSphere, like further relaxed co-scheduling, SMP XenApp VM’s are no longer a problem. If you are using a host with Intel Nehalem CPU’s enable the CPU and Memory hardware assistance (more information on this in part II).
Disk I/O
The second important resource is disk I/O. This will be further explained in the next part of this article but for now I recommend to use two virtual disks for a XenApp VM. One for the operating system and one for the applications. For optimal disk I/O performance, make sure you align the file system in the guest OS.
Memory
The next resource for the XenApp VM is memory. With memory there is one simple rule. Don´t over commit memory for your XenApp VM´s. Depending of the workload of the XenApp server, configure the XenApp VM with the corresponding amount of memory. In most situations this will be 4096 MB of RAM (assuming you are using a 32 bit OS). Make sure you also make a memory reservation of the same size. This way the XenApp VM has all the configured RAM available and the VMware balloon driver cannot degrade the performance of the XenApp VM.
Network I/O
The last resource for the XenApp VM is network. I haven´t seen any XenApp VM implementation where network i/o results in a bottleneck but for best results use the new VMXNET 3 vNIC. The VMXNET 3 has less impact on the CPU which is always useful.
Other considerations
I recommend to use Windows Server 2003 R2 x86 for building the XenApp VM. Windows Server 2008 uses a lot more resources. This probably will be a lot better with Windows Server 2008 R2 but at time of writing this article, XenApp is not certified for use with Windows Server 2008 R2. Furthermore I recommend to remove the CDRom drive and floppy disks. The floppy disk can be complete disabled in the BIOS of the VM. Always install the latest VMware Tools to provide the optimized drivers for the virtual SCSI and network devices and install the balloon driver.
So let’s summarize the preferable XenApp VM configuration:
2 vCPU
4096 MB of RAM with 4096 MB reserved
1 LSI Logic Parallel SCSI controller
2 virtual disks, one of OS and one for applications
1 VMXNET 3 vNIC
CDRom drive removed
Floppy drive removed
CPU and Memory hardware assistance enabled if using Intel Nehalim processors
Again, depending on your environment another configuration could be more desirable. A consistent server configuration is very important in a XenApp farm so I recommend to build a dedicated template for deploying XenApp VM’s.
In the next part of this article I will look at the application landscape and the underlying ESX host for building your virtualized XenApp farm. Stay tuned!
Posted by Ted Steenvoorden 
Posted by Ted Steenvoorden 
Posted by Ted Steenvoorden 
