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Distributed Power Management to bring power efficiency to vSphere

The Distributed Power Management feature in VMware vSphere will bring benefits to IT shops that suffer from regular server downtime.

VMware's vSphere will fully support the Distributed Power Management feature when it hits the market later this year, but some large enterprises won't be able to use it, users say.

Today, VMware's Distributed Power Management (DPM) feature is only an optional enhancement to VMware Distributed Resource Scheduler (DRS) that is "experimentally" supported in Virtual Infrastructure 3 (VI3). It will be fully supported in vSphere.

The use case for DPM is in companies with email, fax, intranet, and database application that are heavily used during business hours but demand for which drops significantly after hours. In such cases, IT pros can use DPM to consolidate virtual machines (VMs) running those services onto fewer hosts and shut down unused servers. Using DPM this way can reduce power consumption 30% to 35% in a production cluster and even more in test and development environments, according to VMware engineers who discussed vSphere at the New England VMware User Group meeting in Newport, R.I., last week.

DPM useful tool -- for some

While this feature is a useful tool, some challenges will prevent large enterprises from taking full advantage of it, experts and users say.

For starters, DPM shuts down only those servers that aren't in demand. So it is only useful to companies that have downtime; those with capacity constraints "will have little use for it," said virtualization user and "Gabe's Virtual World" blogger Gabrie van Zanten.

"My latest two enterprise customers … seldom have much spare capacity," he said. "The ESX hosts normally are already quite loaded and at night they are also very busy with backups," he said. And "in the smaller enterprises where there is always a struggle for capacity, I don't think DPM will make the difference."

This is the case for a large Minnesota medical center that doesn't have the luxury of idle time. "Since the only lower-usage times we have coincide with our backup windows, there's not really any sense in trying to do something like this," said the organization's lead systems software engineer.

And in data centers that use DPM, memory constraints limit the number of systems that can be shut down, van Zanten added. "On a normal host, memory is usually the first resource we're short of. When the CPU of a fully loaded ESX box is still at 60%, we often run into memory shortage," van Zanten said. "Based on CPU usage, it would be easy to load the host with more VMs, especially at night when the backup has finished. But … a VM also needs memory, and that is where it's going to hurt." The number of hosts in a cluster will also limit how far IT can stretch power savings with DPM, van Zanten said. "DPM and DRS work cluster-wide. With 40 ESX hosts, divided over seven clusters, we have an average of six hosts per cluster. With so few hosts, it will be difficult to free one host completely and put it into DPM mode," van Zanten said.

Shutting off servers a common fear

DPM reduces power consumption by automatically powering off servers whose resources are not immediately required and returning power to when the demand increases again. While DPM powers host boxes off completely, it leaves them in standby mode they can re-awaken quickly when needed.

The problem is, some IT pros believe that frequently powering servers on and off is bad for the equipment. VMware expert Cody Bunch blogged, "In all likelihood, you are powering up and down servers that were designed to be powered on 100% of the time. This can potentially lead to more hard drive and other failures," he wrote. "Hardware manufactures are testing against this. ... So while it's really cool … I would still strongly recommend testing it out before deploying it within your environment."

The wait time to reboot sleeping servers may also worry IT pros, but VMware engineers said systems mode reboot quickly.

Van Zanten agreed that this lag time shouldn't be an issue. "The time it takes to kick back in when business wakes up is no problem unless you have all employees start at the exact same time doing their logins," he said. "But since DPM uses knowledge from DRS, it will know soon enough when things get busy and it's time to fire up an extra host."

With the "experimental" version of DPM on the market today, some users had issues with servers coming back online after being shut down.

Rick Scherer, a vExpert and a VMware Certified Professional who writes virtualization tips on, said he tested DPM at San Diego Data Processing Corp., where he works as a systems administrator using VI3.5 on Sun X4450 servers. "DPM showed a lot of promise; the only issues we ran into were machines failing to come back online from standby mode. However we did expect some issues as DPM was only experimental," he said.

"When it works properly, it successfully migrated virtual machines with DRS, then placed those hosts into standby mode. Then, when additional hardware resources were required, DPM would start the machine backup and virtual machines would move back to that restarted hardware with DRS."

He also said using DPM doesn't affect performance and can be used with any virtualized application.

On the Ars OpenForum IT community board, a VMware virtualization user said the DPM power management feature works well for him.

"I've never had [the wait] be a problem, since it doesn't power down your servers to the point where you're running exactly at capacity. There's always some room for additional resource requirements," he said. "If your resource usage fluctuates so much so quickly that a few minutes for a host to power on is a problem then it may not be for you, or you could track your utilization throughout the business day and script something to keep servers up when needed, I suppose."

Though some IT pros are leery of DPM, aggressive virtualization users will give it a try if they have the resources. "This is just like placing SQL on VMware. Some engineers will trust it, some don't. The ones that don't will find numerous reasons not to do this and will never try," van Zanten said. "As for me, I would start testing it and using it on less important systems as soon as it is available. But then again, I'm a bit of a geek."

DPM in vSphere

Whether or not users take advantage of DPM, vSphere's supported version will be integrated with ESX host-level power management features such as Hewlett-Packard's Integrated Lights Out (iLO) and Dell OpenManage, and it will also support wake protocols, and Intelligent Platform Management Interface, VMware engineers told VMware user group session attendees.

VMware engineers also told users the company is exploring ways to make DPM interact with heating ventilation and air-conditioning, or HVAC, infrastructures and looking at ways to incorporate other metrics into DPM for added efficiency.

DPM will be included in the vSphere Enterprise Edition package for $2,875 per single processor.

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