This article contains information about Technical Deep Dive into Server Sizing for VDI-in-a-Box: CPU.

Background

During the design phase of a VDI-in-a-Box deployment, it is necessary to estimate the number and speed of CPUs required to support the desired number of virtual desktops. Ideally, scalability testing should be performed prior to ordering the hardware, but this is not always possible. In the absence of such testing, the VDI-in-a-Box team has conducted real-world testing using LoginVSI to provide more accurate figures to size servers for use with VDI-in-a-Box. The goal of these tests was to constrain only one resource required for virtual machines to run properly. In these tests, the CPU was constrained.

CPU Requirements

Server 1 Specifications

• Dell R620

• 2x Intel E5-2620, 2.00 Ghz, 6 cores each. (24,000 Mhz total computing power)

• 224 GB Ram

• 10x 10k SAS drives in Raid 0

• PERC H710P Mini Mono 1GB RAID cache

• Virtual Machine Operating system: Windows 7 32-bit

• 1 vCPU

• When running LoginVSI Medium load: 1.5GB Ram

• When running LoginVSI Heavy load: 2.0GB Ram

• Hypervisor: XenServer 6.2

LoginVSI 3.5

CPU tests were performed with a server running two Intel Xeon E5-2620, 2.00Ghz, 6 cores each for a total of 12 cores and 24,000 Mhz. CPU turbo mode was disabled.

When running LoginVSI Medium load (Knowledge Worker), the Citrix Technical Support Engineers were able to run 94 desktops without exceeding resource capacity. That approximates to 255 Mhz per desktop when hyperthreading is enabled.

When running LoginVSI Heavy load (Power User), the Engineers were able to run 45 desktops without exceeding resource capacity. That approximates to 533 Mhz per desktop when hyperthreading is enabled.

LoginVSI Medium Load

LoginVSI Heavy Load

Server 2 Specifications

• Dell R720

• 2x Intel E5-2680, 2.70 Ghz,, 8 cores each. (43,200 Mhz total computing power)

• 192 GB Ram

• 14x 10k SAS drives in Raid 10

• PERC H710P Mini Mono 1GB RAID cache

• Virtual Machine Operating system: Windows 7 32-bit

• 1 vCPU

• When running LoginVSI Medium load: 1.5GB Ram

• Hypervisor: ESXi 5.1

When running LoginVSI Medium load (Knowledge Worker), the Engineers were able to run 144 desktops without exceeding resource capacity. That approximates to 300 Mhz per desktop when hyperthreading is enabled. This does not represent the maximum number of desktops that could be run on this server.

144 represent the maximum number of desktops that could be created, based on the amount of RAM available.

LoginVSI Medium Load

More Information

Hyper-threading adds approximately 50% increase in performance so if hyper-threading is disabled, multiply the Mhz per desktop requirement by 1.5.

These figures apply to Pooled Desktops only. Testing has shown that Personal Desktops incur a processor performance overhead and can reduce packing density by 14%. If Personal Desktops are being used, multiply the Mhz per desktop requirement by 1.14.

Scale Up or Scale Out?

During the design phase of a VDI-in-a-Box deployment, a decision must be taken to scale up by using more powerful CPUs or to scale out by adding an increased number of less powerful CPUs. Following are some of the considerations to aid in that decision process:

• Datacenter Resources – The datacenter hosting the VDI-in-a-Box Servers might have limited physical space, electricity, and cooling. If any of these resources are limited, scaling up is a better option.

• Licensing Costs – While two out of the three hypervisors that VDI-in-a-Box supports are available without charge, vSphere requires a paid annual license. If licensing costs are a factor, scaling up is a better option.

• Redundancy – Spreading user load across more, but less powerful servers helps reduce the number of users affected from the failure of a single host. If the deployment requires high availability, then scaling out is a better option.

It is also important to note that scaling out a VDI-in-a-Box deployment is very simple and only requires four steps:

http://support.citrix.com/proddocs/topic/vdi-54/vdi-configuring-grid-xen.html