Client-hosted virtualization engages the native capabilities of the mobile device, instead of just using a laptop as a terminal for a remotely running Windows session on a server. The distinction is not lost on server-virtualization specialists, such as Citrix Systems Inc., Microsoft Corp. and VMware Inc., that also offer client-hosted solutions.
VMware, for example, offers Local Mode in the VMware View VDI; Microsoft offers Enterprise Desktop Virtualization (MED-V). Both, however, are a Band-Aid on server-side virtualization rather than a switch to client-hosted solutions.
VMware View sidesteps the always-online requirement of server-hosted virtualization by allowing users to check out their desktop image to a laptop, then check it back in when they return from the road—at the expense of about 30 minutes to perform the transfer.
Microsoft’s MED-V similarly sidesteps the compatibility problem with old apps by allowing a second, older operating system—usually Windows XT—to run in a virtual environment on the client’s otherwise Windows 7 PC. Microsoft also offers Application Virtualization (App-V) and User State Virtualization (USV), which it claims collectively complete the picture for mobile users wishing to access business data and programs from their laptops.
“Any virtualization technique still needs to manage the environment, whether it’s the applications, the operating system or the user’s state,” said Karri Alexion-Tiernan, director of desktop virtualization at Microsoft. “We work really hard to provide the tools needed for complete desktop-to-data-center management.”
Citrix, whose XenDesktop server-hosted virtualization platform hosts millions of users worldwide, has added XenClient for laptop users to its XenApp solution for virtual application delivery, touting a comprehensive client-hosted solution that overcomes the shortcomings of server-side virtualization.
“XenDesktop is our flagship for server-hosted virtualization, but it also works with XenClient and XenApp,” said Peter Blum, director of product management for XenClient at Citrix. “For highly mobile users and for high-security environments, XenClient makes sense. But there is not one type of virtualization that fits all situations.”
Citrix became an early investor in client-hosted virtualization in 2009 when it took a share in Virtual Computer.
Hypervisor at the switch
Client-hosted virtualization installs a hypervisor software layer to switch between separate binary images without rebooting. An image consists of an operating system and its application programs, with the user’s state also switched but saved separately. Type-one hypervisors, which install directly on the “bare metal” of a laptop or server and then layer the virtualized OS and apps on top, can run a virtualized OS just as quickly as without virtualization. Type-two hypervisors, added above a traditional OS—for instance, to let Macs run Windows apps—incur a performance penalty when threading one OS’s commands through the other OS.
Virtual Computer is giving away its type-one NxTop hypervisor free for personal use, betting that corporate customers will like it enough to invest in its server-hosted software for managing up to 1,000 virtualized PCs with a single server. MokaFive, RES Software, Symantec Corp. and Scense BV are also hawking variations on client-hosted virtualization.
Because client-hosted virtualization allows a master image—an OS and its apps—to be centrally managed and bidirectionally synced with users’ devices, it lets IT retain control of all mobile resources, while providing services such as tracking user states so that the user’s computing environment can be restored if a laptop is lost or stolen. “Especially for smaller companies, client-hosted virtualization offers many of the same benefits as server-hosted virtualization, such as remote management, on-the-fly re-imaging and maintaining standardization,” said Sao.
One caveat that has kept larger IT organizations from signing up has been the perceived loss of control over vital databases, which need to be uploaded to laptops for client-hosted virtualization to work. But Virtual Computer announced a storage array network technology, licensed from Lenovo, that permits corporate users to access secure, encrypted data that never leaves its premises, while still allowing client-hosted execution of programs under NxTop.
Lenovo, using Intel’s vPro-equipped processor cores, is close to releasing laptops with the NxTop hypervisor—but no OS—preinstalled. Users will be able to load multiple flavors of Windows and Linux by installing them as usual and using NxTop to switch among them on the fly.
Citrix's FlexCast technology uses the Intel Xeon-powered NetScaler to deliver its
XenDesktop virtual Windows desktop to remote Windows 7 PC users as well as mobile users working on intelligent client devices, all managed from a data center running either Citrix’s own XenServer hypervisor or Microsoft’s
Hyper-V. SOURCE: Citrix
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bRES Software's hybrid desktop management technology supports the full slate
of Microsoft SystemCenter virtualization capabilities, from app streaming to client- or server-hosted virtual desktop infrastructure.SOURCE: RES Software/Microsoft
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A type-one hypervisor is inserted between the physical hardware and a guest operating system (right) here using virtual I/O managed by the host operating system (left). SOURCE: Virtual Computer
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