Citrix XenClient vs. VMware View 4.5 Local Mode -- which is better for your environment?

Offline support for VDI comes in different forms. VMware's Local Mode offers benefits that Citrix XenClient doesn't, and vice versa. Here are the pros and cons of each.

Citrix XenClient and VMware View 4.5 Local Mode appear to be very much alike -- both bring offline support to virtual

desktops, run virtual machines locally on the endpoint, are part of a larger virtualization solution and are critical pieces of technology offered by their respective companies.

However, these client hypervisor products are vastly different in how they operate and are deployed, and those differences may affect which virtual desktop infrastructure (VDI) offering serves your environment better.

How Local Mode and XenClient compare
Citrix XenClient in XenDesktop 5 and Local Mode in VMware View 4.5 both let employees access their virtual desktops from anywhere, so they remain productive even when not connected to the corporate network. Ideally, that solves mobility problems, giving users access to their applications and key features of their computers while traveling or at remote locations without connectivity back to the home office.

With either product, employees using their virtual desktops while disconnected may not have access to corporate resources or databases, but they will still be able to use applications that work fine with local data, such as office suites, design programs and other critical applications.

While both offerings serve essentially the same purpose, there are substantial technical differences between VMware and Citrix's "disconnected" VDI products to consider.

Citrix XenClient
XenClient is a bare-metal (Type 1) client hypervisor that runs virtual desktops directly on client devices and functions while disconnected from the primary network. This solves one of the major problems associated with VDI and giving users the ability to use their virtual desktops anywhere, anytime.

In addition to offline support, XenClient simplifies desktop management and disaster recovery because images of desktops can be easily created, secured, deployed and moved across any supported endpoints.

Since XenClient runs directly on the hardware, it is not dependent on an underlying operating system. That independence results in improved performance and stability, because no additional software layers are needed to translate and pass virtual machine operations down to the base hardware. Ultimately, it eliminates incorrect fault handling or bottlenecks from a host operating system.

What's more, a Type 1 hypervisor eliminates the need to purchase or license a host operating system because it's the first (and only) layer between the guest operating systems and the hardware. Microsoft Software Assurance (SA) customers are allowed to run up to four instances of Windows in a virtual machine (VM), so those customers can use XenClient to run up to four guest Windows environments on a corporate desktop that's licensed with SA.

However, the advantages offered by Type 1 client hypervisors may be offset by a few disadvantages. For example, installing XenClient is a destructive process because it requires removing or overwriting the device's native operating system. Deployment of a Type 1 hypervisor can also be time-intensive because a technician must manually install the product.

In addition, XenClient only works with the hardware virtualization capabilities found in Intel's vPro family of chips, which limits the Hardware Compatibility List to endpoints equipped with Intel's proprietary virtualization technology.

VMware View 4.5 Local Mode
VMware introduced Local Mode with VMware View 4.5 to give users disconnected virtual desktop access. Like most disconnected virtualization technologies, Local Mode works by running a hypervisor on the endpoint, which supports desktop virtual machines even when there isn't persistent corporate network connectivity.

Unlike XenClient, Local Mode is a Type 2 client hypervisor, which runs on top of a compatible host operating system on the client device instead of running natively on hardware.

That reliance on a base operating system affects performance because the hypervisor relies on the host OS to translate actions from the guest OS (the VM) down to the hardware. That additional layer affects throughput, performance, stability and several other factors that may hurt the user experience.

What's more, technology based on Type 2 hypervisors tends to require additional memory, storage space and management, because target machines need to have enough available resources to run the native OS, the hypervisor and the guest OS. That may increase the cost of the endpoint.

Nonetheless, Type 2 hypervisors do offer a few advantages over Type 1 hypervisors.

With VMware's Local Mode, installations are simpler because a destructive install is not necessary; View is simply installed on the existing OS without any hands-on work. VMware View also works with a broader spectrum of hardware, because as the endpoint is running a supported OS, Local Mode will work fine. Other advantages include the ability to run multiple virtual machines on a single device, easily copy VMs from one system to another, and quickly remove a VM from an endpoint.

Simply put, VMware View 4.5 Local Mode offers enhanced flexibility, increased hardware support and a simplified installation, but it does not offer the same levels of performance as a Type 1 hypervisor and may require additional memory and processing power to give an acceptable end-user experience.

Meanwhile, XenClient offers excellent performance and improved stability at the cost of limited supported hardware and destructive installation requirements.

ABOUT THE AUTHOR
Frank Ohlhorst is an IT journalist who has also served as a network administrator and applications programmer before forming his own computer consulting firm.

This was first published in February 2011

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