When constructing a VDI project plan, experts and early adopters advise data storage administrators to start with...
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a pilot or test program to gauge the changes and costs associated with a virtual desktop infrastructure (VDI).
With VDI storage, desktop operating systems are hosted inside a virtual machine running on a centralized server. While this makes it easier and cheaper to manage and secure data, it changes the game for storage capacity, performance and administration.
Because it requires hundreds or thousands of desktop images to boot simultaneously, VDI brings about things like boot storms that stress a storage system and often changes the way storage is provisioned, backed up and recovered, replicated and secured.
VDI adoption involves steep I/O demands
The steep I/O performance issues associated with VDI adoption almost always require networked storage, but solid-state drives (SSDs) and a large cache are also recommended. However, these technologies bring additional costs to an organization's IT infrastructure.
"A virtual desktop infrastructure requires a different style of storage than what people might be used to," said Ray Lucchesi, president at Broomfield, Colo.-based Silverton Consulting Inc. "VDI begs for enterprise-class storage."
Sam Lee, senior solutions architect at systems integrator Force 3, said storage I/O becomes a major performance bottleneck in a typical VDI deployment, and recommends using SSDs and spreading the workload.
A storage system for VDI needs to be able to handle peak I/O for all users simultaneously at certain times, such as when most users' log on in the morning or log off at night. Lee said SSDs must also be load-balanced for peak efficiency. To run smoothly, Lee said, VDI can require approximately 20 to 100 IOPS per desktop during peak times.
"A lot of people vastly underestimate how much I/O a single desktop can use," he said. "When you use VMware View or Citrix Provisioning Server, they make a writable snapshot. That's what a virtual desktop is. Every snapshot on every desktop reduces space but increases the load on storage I/O because you centralize the I/O to one or two LUNs. When you have 150 desktops on one LUN, that LUN gets oversaturated."
According to Lee, "you have to spread it out; you can't have a single SSD for 1,000 users. On a Fibre Channel disk, you can probably put three VDI users per spindle on a 10K drive and five users per spindle for a 15K drive. You can get about 200 users per SSD LUN."
VDI and thin clients improve log-in times, cut costs
Slumberland Furniture in Little Canada, Minn., has been using virtual desktops via thin clients on its showroom floors for approximately seven years, and added its first SAN in late 2006. Slumberland uses Compellent storage systems with Cisco Systems Inc.'s Cisco Unified Computing System (UCS) and Windows Terminal Services for thin clients. Seth Mitchell, Slumberland Furniture's IT manager, said his VDI farms can require 7,000 to 9,000 IOPS. He expects to add SSDs to the Compellent systems next month, but has avoided I/O problems by using 10 Gigabit Ethernet (10 GbE) connectivity and spreading the load across enough Fibre Channel drives.
Mitchell said his current setup supports 160 VDI user sessions per server, allowing one administrator to handle 1,000 clients while giving sales people on the show floor faster access to information.
"We have quite a few disks because we're latency sensitive and IOPS hungry," Mitchell said. "We started with 64 disks on our top tier; now we're at 80 disks. We get enough IOPS without any trouble. We have yet to even make it sweat. Our log-in time is greatly improved with VDI; it used to take 50 seconds to log in, now it's seven or eight seconds for a typical user."
One IT manager for an insurance provider said he migrated over 12,000 users globally to Citrix thin clients for a VDI project as part of a data center overhaul that included consolidating to three primary data centers from eight. He estimates the new setup has saved about $10 million so far and projects future savings of about $50 million.
The insurance firm uses EMC Corp. Symmetrix storage and Silver Peak Systems Inc.'s NX-8504 WAN optimization devices to reduce latency. The manager, who asked not to be identified because company policy prohibits him from speaking to the press, said VDI and a good remote access solution makes his disaster recovery (DR) situation easier to manage.
"One of the benefits we find from desktop virtualization is that I can now support remote users as if they're local. I give them a desktop if they're at home or sitting in the airport just like I could if they were in the office," he said. "That's totally changed the way we approach DR. I can have people work from home instead of bringing them into a temporary DR site or setting up a permanent DR site in a nearby building."
Still, he doesn't anticipate moving the entire company to VDI.
"We see it as a specialized solution for high-profile users," he said. "For the typical rank and file call center people, no, we won't go to the expense of rolling out VDI. For people who need a custom programming language or are doing application testing, that's where we see virtual desktops."
VDI proof of concept: Which applications are best for VDI?
In its "Storage for VDI Buyers Guides: Planning and Considerations & Storage Systems" publication, Broomfield, Colo.-based analyst firm Evaluator Group Inc. said good candidates for a VDI project plan are sales force automation (telephone sales, customer service), knowledge workers (designers, developers and engineers) and officer workers who share a standard set of applications.
Many organizations are easing into VDI by piloting it for specific applications or a group of workers who fit one of the above categories.
Brian Diegan, vice president of network services at Hermitage, Pa.-based First National Bank (FNB), said his bank is doing a VDI proof of concept for an application used by its tellers across 300 locations. He expects the most common application for tellers to load within three milliseconds to four milliseconds vs. the approximately four seconds it now takes. FNB uses VMware for server virtualization, but Diegan said he would probably use Citrix for VDI because it makes better use of bandwidth.
"The biggest challenge of VDI is bandwidth for us," Diegan said. "We have 700 tellers, and we have to work through a learning curve with them. We don't want anything to change for them."