The high cost of shared storage has always been a trouble spot for those considering server virtualization. When it comes to hosting desktops with VDI, associated storage costs are often a deal-breaker.
However, new tools and technologies have emerged to ease storage costs for hosted virtual desktops. The tools come from third-party virtualization management vendors, storage vendors and from the virtualization players themselves.
Without using any of these tools and technologies, storage costs can consume 40% to 50% of a virtual desktop infrastructure (VDI) project's overall cost, said Jeff Byrne, senior analyst at Taneja Group, headquartered in Hopkinton, Mass. In fact, one shop's total cost of ownership (TCO) analysis for a VDI implementation estimated a per-seat cost of $3,000, with $1,600 of that going toward storage space on the storage area network (SAN), he said.
Post-factum VM optimization
At the University of Wisconsin's Department of Orthopedics and Rehabilitation, storage costs for its virtual environment were high enough to send Ken Fanta, the group's IT manager, looking for answers.
The department had previously shared its IT resources with another part of the university. In setting up its own infrastructure, Fanta decided to virtualize. "We were a totally greenfield environment," he said. By setting up systems in a virtual environment beforehand, the department could gracefully transition to the new environment in one fell swoop.
Fanta and his team configured VMware ESX running on six Hewlett-Packard DL385s with 32GB of RAM, connected to an HP EVA SAN. The environment hosts 160 virtual machines -- 30 for server applications and the remainder as dedicated VDI desktops.
Once the environment went live, however, Fanta said he noticed that he had overallocated space on many of his VMs. "On Fibre Channel SAN storage, this can get kind of expensive." Unfortunately, while VMware's management tools make it easy to add space to a virtual machine, "there's no easy way to take it back," added Fanta.
Fanta found a tool from Vizioncore that could help identify wasted space in his VMs and resize them downward. The tool -- vOptimizer Pro -- also optimizes Windows XP for use in VDI scenarios. "It seems to do a really good job of that," Fanta said. All told, vOptimizer Pro helped Fanta reclaim over 1 TB of wasted capacity. When you consider that the team paid just over $3,000 for vOptimizer versus $3,600 per TB of SAN space, the tool has paid for itself and will continue to pay dividends as it recommends changes over time, he said.
Storage vendors have identified ways to help take the sting out of a costly VDI implementation. Enterprise SAN vendor 3PAR Data Systems, for instance, offers a version of its thin provisioning and snapshot software configured specifically for VDI environments. Called Thin Copy Desktop for VMware VDI, the tool takes a thin-provisioned LUN containing a VDI golden image and creates writable snapshots of it. Those snapshots are then presented back to the ESX host. Up to 128 VDI instances can be created from a single golden image.
The result is an environment that takes about one-tenth the space of a traditional "fat" provisioned environment. Thus, a 100-user VDI environment that might usually consume 15 TB of disk space could be achieved with 1.5 TB of capacity with room for growth, according to 3PAR.In addition, since most 3PAR customers tend to purchase a Thin Copy license as part of their array, there is little additional cost associated with trying out VDI, the company said.
Another storage vendor, NetApp, takes it one step further with its deduplication technology, which identifies commonality between blocks of storage and stores them only once. Deduplication can be used across a number of different types of virtual desktop configurations, said Vaughn Stewart, NetApp infrastructure virtualization consultant.
In VDI environments where user data has been separated from the operating system and applications, deduplication can result in a storage savings of 35% to 60%, he said. Environments that maintain a dedicated virtual machine, complete with operating system, application sets and user data for each end user, can see even greater savings -- on the order of 75%, Stewart said.
Going to the virtualization source
Ultimately, most enterprise IT shops will probably turn to the virtualization vendors themselves for a solution to their VDI storage ills, said Taneja Group's Byrne. Options include the View Composer feature in VMware View 3 or Citrix Provisioning Server, an operating system streaming technology that comes with certain versions of XenDesktop. With the View Composer feature in View 3, VMware claims a 90% savings in storage and management costs over traditional VDI configuration approaches. The feature relies on Linked Clones snapshot technology, which is included in its base platform to quickly copy virtual desktop instances from a single golden image.
Likewise, Citrix has a technology that can also achieve 90% space savings: Provisioning Server, which is bundled with XenDesktop Advanced Edition. Rather than use cloning technology, Provisioning Server takes a single golden image and streams it to a desktop when a user signs on, according to Citrix.
Host-based offerings such as VMware's and Citrix's are more tightly integrated with the underlying virtualization platform than a storage vendor's solution, and may be easier to work with, said Byrne. View 3, for instance, "is optimized with vCenter, has a familiar interface and provides accelerated desktop provisioning," he added. With Linked Clones' Recompose feature, when an administrator takes a golden image "at the top of the tree" and applies a patch to it, "all downstream desktops will all be updated to reflect that top-level image. If you're a VMware admin, it's pretty clear you'll want to go with View," Byrne said.
However, VDI shops will have to weigh the potential storage capacity savings against additional licensing costs for View Composer or Provisioning Server. List price for the baseline VMware View 3 Enterprise Edition is $150 per seat, but the price jumps to $250 per seat for the Premier Edition, which includes View Composer. Similarly, Citrix XenDesktop Advanced Edition, which includes Provisioning Server, lists for $195 per seat, compared to $75 per seat for the Standard Edition.
Let us know what you think about the story; email: Alex Barrett, News Director.