Client hypervisors let end users access their virtual machines (VM) offline when network performance is poor or nonexistent. The technology plugs a gap because end users today have no choice but to connect to a network to access their virtual desktops.
"The client hypervisor is just another layer that was missing from VDI [virtual desktop infrastructure]," said Shannon Snowden, a Citrix Technology Professional and consulting partner with Louisville, Ky.-based New Age Technologies. "Desktops are not 'one size fits all.' There is a need that this meets, and some people will want to snatch this up to fill that need."
Snowden said he expects people to use XenClient as a supplement to XenDesktop in the same way that people use XenApp for application virtualization. It may also be viewed as a good alternative to server-hosted virtual desktops, he said.
Citrix's XenClient also offers a cost-savings proposition because, instead of storing hundreds of gigabytes of VM images on a server, as required with VDI, IT pros can allocate VMs to the endpoint hardware and run them like regular PCs, one analyst said.
VMware is also working on a client hypervisor, but slowed its development in favor of "client-mode," a Type 2 hypervisor that will provide offline support for VMware View 4.5 when that product hits sometime this year.
Client hypervisors are here before their time
But with very little ecosystem support for client-side virtualization technologies and slow adoption of desktop virtualization itself, client hypervisors will launch ahead of their time.
In fact, people are just getting up to speed on the various server virtualization offerings and haven't given desktop virtualization a thought, according to Harpreet Walia, founder and chief technology officer of WaveStrong Inc., a Dublin, Calif.-based IT services firm.
"[Client hypervisors] will be good for VDI, but these companies are coming out with products faster than customers can understand them," Walia said. "It will take some time before people even figure out what they are good for."
When client hypervisors do hit the scene, they could play an important role in desktop virtualization adoption, because it gives users a traditional PC experience but gives IT pros a way to manage desktops from the back-end, said Chris Midgley, CTO of start-up desktop virtualization management company Unidesk in Malboro, Mass.
XenClient vs. VMware Client Mode
XenClient is a Type 1 "bare-metal" hypervisor that runs below the operating system layer. VMware's "client mode" is different from a client hypervisor in that it runs an offline VM on top of the existing operating system (Type 2). Because the client hypervisor lives beneath the OS, it is not vulnerable to OS-related problems.
One analyst, who asked not to be identified, referred to an OS-based, Type-2 hypervisor a "cop-out," and those interviewed said a bare-metal hypervisor is a better bet.
"The further you can disassociate from the OS, the better," Snowden said.
By running below the operating system layer, Citrix XenClient will be OS-agnostic, and VMs will be able to move around without conflict. Snowden said it will probably perform better than an OS-based hypervisor because it runs directly on the resources it needs.
It should be noted that Citrix and VMware aren't pioneering new territory with client hypervisors; products already exist from small companies, including NxTop from Virtual Computer in Westford, Mass., and NeoSphere from Neocleus in Cambridge, Mass. Both products offer a Xen-based client hypervisor and back-end desktop management.