That's a big problem for traditional storage arrays because many don't have enough cache to keep up with the influx of data, and cache misses occur, slowing down the system.
How to deal: First, perform an I/O profile analysis to make sure you know what the I/O demand is going to be. "A general rule of thumb is that to support a typical user on [a virtual desktop infrastructure] in a steady state environment, you need ... 20 to 40 I/O per second per user," Candelaria says. "If you don't account for that I/O demand, your user experience is going to suffer drastically."
Also, make sure you have a storage fabric and a transport fabric that's going to scale. "I see a lot of customers attempt to do virtual desktop projects without a high-speed storage fabric, and they're continually maxing out 1-gig storage links running on SCSI," he says. "You need to look at a higher-speed transport like 10 Gigabit iSCSI or Fibre Channel."
If you're going to deliver virtual desktops to remote users, make sure you have enough bandwidth to ensure a favorable user experience.
Finally, make sure you have a substantial amount of write I/O, Candelaria says. If designed correctly, the desktop workload is predominately write I/O as opposed to read I/O. Traditional vendors like Citrix and VMware have come up with ways to mitigate read traffic from hitting the array, and they don't have to reach back to the array for data, reducing the amount of redundant traffic that it sees.
On the backup side, a handful of vendors are building backup and recovery tools for the virtual environment that runs within their virtual infrastructure. That way, the vendors can capture and manage data right on top of the physical server and optimize it before it ever leaves the virtual server.
Acronis, for example, recently announced a product that can back up virtual machines in a matter of minutes and recover the data in about the same amount of time, while keeping data organized as virtual servers move around. Many vendors have harnessed some virtualized infrastructure capabilities, such as storage snapshot tools and replication, to make backup simpler and faster than was possible in the past.
When the Bank of Fayetteville in Arkansas first started virtualizing its servers, Les Barnes, senior vice president and IT manager, treated backups the same way he would with traditional servers: He used a tape library. But after a few months, he knew there had to be a better way. What's more, backups were traditionally performed overnight, but as more customers demanded 24/7 access to the online banking system, Barnes needed another solution.
He completely eliminated traditional backups and replaced them with SAN replication and SAN snapshots as a way to make multiple copies of SANs off-site.
"The beauty of using SAN replication is that it completely offloads any I/O from the server," Barnes says. "It's now SAN-cluster-to-SAN-cluster communications. It's all back-channel stuff. There is no impact on the end user or the virtual machine. And if I have to recover, I can do it in a few minutes rather than a few hours or a couple of days."
Elam looks at Arnold Worldwide's SAN as a way to bring backups forward. "It's almost impossible now to just write everything to tape [over the weekend]," he says, adding that the ad agency holds 60 terabytes of data on its SAN. "But because we're replicating a lot of stuff off-site, that kind of serves as a backup. We also have snapshots that we keep live. We also do deduplication to get backups in a timely window."
But Elam warns that those snapshots can be quite large: "The biggest thing we didn't realize when we rolled this out was the amount of space that snapshots or replays take up. We didn't even think about how much it takes. You need to plan for that in the amount of data storage you have."