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Putting too much stock in VDI IOPS could lead to project failure

When carrying out a virtual desktop infrastructure project, providing an adequate number of IOPS for each desktop is essential to keep business processes running smoothly. Unfortunately, determining what that number of IOPS should be is often a daunting task for virtualization and storage administrators.

Accounting for spikes in demand due to morning log-ons or frequently accessed applications makes it difficult to anticipate how many IOPS each user will need to see adequate performance. But focusing too much on the average number of IOPS can be dangerous, virtual desktop infrastructure (VDI) expert Brian Madden told attendees during his presentation at TechTarget's recent Storage Decisions Seminar in New York. According to Madden, it's a common way storage can kill a VDI project.

"It's still totally unknown how many IOPS a VDI desktop actually does need," Madden said, despite tools such as VDI IOPS calculators that aim to help administrators determine the cost of a VDI project.

Madden explained that as a starting point, IT professionals often use these resources by estimating factors such as the number of IOPS they'll need per desktop, desktops they'll have per server and the number of servers per host in order to get a rough idea of the cost. To estimate the number of IOPS needed per desktop, they often average the activity over a given workday.

The problem with this, Madden explained, is that "In no way do these numbers relate to what people need in the real world. It's like a false statistic."

He cited aspects including I/O spikes and inactivity during lunch or off-hours as skewing the numbers too far to rely on them.

"Finding the average over a 24-hour period wouldn't really work because you're only working over one-third of that period. What about over an 8-hour period? Do I include log-ons and log-offs?" he asked.

"My point is, whatever number of IOPS you decide a Windows desktop needs, you have to support that many IOPS all at once. The good news is today's storage technology can do that. But you can't look at it like 'I have 200 users so an average of 40 IOPS is probably good,'" he said.

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