As virtual desktop infrastructure (VDI) gains traction among enterprises, storage pros are finding that administration of centralized data center storage to support virtual workstations in enterprise environments requires new approaches to capacity planning and performance management.
Centralized application deployment for workloads has been available for years through products that allow users on desktops and laptops to share access to data and applications through a centralized server. Newer products hitting the market, such as VMware Inc.'s VMware View and Citrix Systems Inc.'s XenDesktop, also centralize application data and operating system images in the data center infrastructure, but create personalized images served to each user's workstation instead of sharing one image among many. Done correctly, virtualized workstations can cut down on the time IT spends supporting endpoint devices and potentially improve the security and efficiency of endpoint devices.
A recent survey of 480 IT decision makers in North America and Western Europe conducted by the Milford, Mass.-based Enterprise Strategy Group (ESG) found virtual desktops have yet to take over most enterprise data centers, but VDI has gained traction among IT staffs looking to optimize their current PC environments. The survey found 21% had a VDI implementation in either production or test, 8% were planning deployments and another 31% were considering the technology.
Additionally, according to the ESG report, "current VDI deployments are limited in scope, but growth is expected." So far, most of those surveyed have virtualized fewer than 10% of their client devices, but 45% said they expect to have virtualized more than half of their client access devices within three years.
Virtual desktop infrastructure deployment carries some of the same storage efficiency challenges as server virtualization in general, including data growth resulting from the storage of many similar operating system images. Storage technologies such as data deduplication can help organizations retain control over data growth, but other steps may be necessary to maintain adequate performance.
Jeremy Page, systems architect at gas pump equipment manufacturer Gilbarco Veeder-Root, based in Greensboro, N.C., said his company has 120 virtual desktops in production after four years of working with VMware's VDI software. The company has clustered NetApp Inc. FAS3070 and FAS3020 filers at its headquarters and a disaster recovery (DR) site, and Page said he uses NetApp's built-in primary storage data deduplication to reduce the data footprint of those virtual desktops "down to 8% of the actual space."
However, "instead of a space limitation comes an IOPS limitation," Page said. With desktop images compressed onto a smaller number of disks, "boot storms" -- in which most of the desktops on the system request images from centralized storage at the same time -- can cause performance slowdowns unless provisioning is done carefully. "We spread the load by making really big groups of 18 disks per RAID group, and multiple RAID groups are shared by virtual workstations and VMs [virtual machines]," he said.
Page also recommended using NFS as the storage interface protocol rather than Fibre Channel (FC) or iSCSI. "With NFS, we can use snapshots to roll back to a good server image and have it set up and restored quickly – with traditional Fibre Channel or iSCSI linear backups, that can be a little more complicated," he said. "Make sure you know what you're doing for backup purposes – if VDI is rolled out right, data won't be stored at the desktop and shouldn't increase backup workload."
But ESG senior analyst Lauren Whitehouse said many enterprise IT organizations don't back up workstation data, and pulling desktop images onto centralized storage might create an unexpected task for the backup team. "Devices that may not have been centrally protected become the data center's responsibility," she said. "That can create problems for organizations, particularly if they're not adjusted to backing up for VDI."
One administrator in a large VDI environment said his IT staff still doesn't back up desktop data, though it lives on data center storage. "If an individual desktop goes down, we're just going to assign the user to a new one and reinstall their applications," said Chris House, senior network analyst at The MetroHealth System, a hospital network based in Cleveland. MetroHealth uses 1,500 VMware virtual desktops and stores data on a Hewlett-Packard Co. StorageWorks XP1024 high-end disk array.
House said the initial VDI deployment was done using a midrange HP StorageWorks EVA8000 array, but with more than a thousand desktops, the IOPS required pushed it up to tier 1 storage. "The VDI environment was averaging between 4,000 and 9,000 IOPS most of the time, but once a week at 2 a.m. it would spike to 40,000 IOPS," he said.
The spike was accounted for by an inventory scan process that involved all the desktops. "The [XP] array can handle it, but you lose some ROI going with more expensive storage," House said.