Capacity planner limits VMware consolidation ratio

Capacity planning guru Tom Becchetti explains his less-is-more philosophy of deploying virtualization in the data center.

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Not all virtualization practitioners strive for extreme virtual machine-to-server consolidation ratios. IT administrators that value uptime and stability over maximum server efficiency might want to consider keeping the number of VMs (virtual machines) per server to a dull roar, said one VMware user.

Tom Becchetti is senior capacity planner for a large Midwestern financial services firm and oversees 700 Windows and Linux servers with his colleagues. Of those, about 165 are VMs, spread across 40 VMware ESX 2.5 and three VMware ESX 3.x nodes.

"We shoot for a consolidation ratio of 8:1," Becchetti said. Currently, though, his ESX nodes are running at about a 4:1 ratio, leaving plenty of room for growth.

That ratio may increase as Becchetti's firm starts populating its data center with new dual processor, dual-core Dell 6950s, and retires its Dell 2850s. In that case, "it might be OK to push it to 12, 16 VMs," Becchetti said. With 16 GB of RAM per server, a 16:1 consolidation ratio still falls within the range of the 1 GB-per-VM rule of thumb.

On the storage side, Becchetti is equally reserved, pairing a maximum of eight physical ESX servers per storage area network (SAN) array, rather than the 16 advocated by less conservative shops.

The reason? To avoid performance and availability problems down the road.

"As a system administrator, you don't want to get called at 2:00 A.M.," Becchetti said. "Not being greedy is what keeps us from having problems."

Becchetti's firm has also taken a measured approach to upgrading from ESX 2.x to the latest VMware Infrastructure 3. Currently, the three ESX 3.x boxes in Becchetti's shop were installed net-new, and he plans to upgrade a few systems on an as-needed basis. The rest, however, will move up "through the stepping stone process – as things start dying, you sunset them."

Migrating from ESX 2.x to 3.x isn't something you do lightly. It's work, and as Becchetti said: "We don't like to do extra work if we don't have to."

This easy-does-it upgrade philosophy is common among VMware administrators, said Bogamil Balkansky, VMware director of product marketing for VMware Infrastructure 3. "Customers don't tend to do big bang upgrades, they tend to upgrade in batches," he said.

Reduced workload
In the long run, introducing VMware virtualization into his shop has reduced the IT staff's workload, Becchetti reports. "There was an expenditure in the learning curve, but we're starting to feel like we have a handle on things."

For one thing, managing performance and uptime is easier in a virtual environment, he said. Using tools like VMware VirtualCenter, "I can run through our farm and easily look for resource constraints, then drill down and really easily find, say, a runaway Windows process."

For non-virtual servers, service and performance management in Becchetti's shop is the province of ProactiveNet, a business services management (BSM) platform from ProactiveNet Inc., in Santa Clara, Calif. But so far, that framework has only been of limited utility, Becchetti said, because it produces too much "noise" and because not all his systems have been outfitted with an agent.

Virtualization has also reduced the staff's hardware maintenance duties. "We have far less hardware to take care of – we spend less time replacing failed hard drives, DIMMs, power supplies," said Becchetti.

And that, ultimately, saves both time and money, Becchetti said. "It all comes down to what's more expensive – people are hardware?"

Let us know what you think about the story; email: Alex Barrett, News Director

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