Power in the Data Center: To Put a Watt In, I Must Take a Watt Out

It’s interesting talking to customers about power in the data center, because they have such wildly varying perspectives. Some say that power doesn’t really matter at all, and they wonder what the big fuss is. Others say power is the single most critical issue in their data center, and they are surprised that anybody might not agree.

The folks who say power doesn’t matter either haven’t thought about it much, or else they tell me that they’ve done the math, and the cost of keeping their spindles spinning just isn’t that high compared to the cost of buying and managing the storage.

The ones who say power is critical typically can’t put any more power into their data center. In some cases they literally can’t get more power – the power company won’t sell them any more. In other cases, they’ve hit limits on the wiring or the cooling in their data center.

A financial customer in New York explained it best: “We’re at 100% of power capacity today. For every new watt I bring in, I’ve got to figure out how to take one out.” He was very interested in upgrading to new storage systems that consume fewer watts-per-terabyte.

He was also interested in VMware, since that often drives large power savings. (See this blog on how one customer used VMware to reduce power by 450 kW/month.) In most data centers, servers consume more power than storage, so most people start there, but consolidating storage is the obvious next step.

There are many ways that storage companies can help you reduce power, but – surprisingly – more efficient hardware is low on the list. We all take about the same power to keep a spindle spinning, because we all use pretty much the same disks, power supplies, processors and so on.

On the other hand, it takes roughly the same power to run a 144 gigabyte FC drive as a 750 gigabyte ATA drive, so using the largest drives possible is a great way to save. To use ATA drives for mission critical data, you’ll want a RAID that protects against double disk failures. Any feature that improves utilization will also reduce power. Use RAID instead of mirroring. Use thin provisioning. Use clones or snapshots instead of full copies. (For details, check this paper which has point-by-point recommendations for reducing storage power consumption. This paper describes what NetApp’s own IT team did to save power.)

To summarize, the biggest savings don’t come from hardware, but from software features that improve storage efficiency and storage utilization.

What I love about all of this is that self-interest actually drives customers to a greener data center. One of my frustrations with corporations is that economics often seem to trump “good citizenship”, so I love it when economics actually drive companies to do the right thing.

Comments

[Matt]

Dave, the people who don't think power consumption is a problem are the ones who don't see the energy bill. If it doesn't benefit the storage or server admin to operate more energy efficiently, they're not going to see it as an issue.
Data Center Blog: Server Specs

[Dave Hitz]

Blake: Thanks for the correction! Yes, I meant gigabytes and not terabytes. It's fixed now.

Alex: I agree completely. A handful of big disks won't provide as much performance as many small ones. So you can't always move, but for data with lower performance requirements, there is an opportunity to save lots of power.

As John points out, an automated policy engine can be a good way to find and move rarely used data that probably doesn't need so much performance.

[John McArthur]

Dave, I couldn't agree with you more. I would add to your list, however, de-duplication and deletion. A simple tool to view files by age, filetype, user, creater, and last use, combined with a policy engine for migration and deletion can go a long way to cleaning up the data cabinet. And we need the IT department, not the facilities director, to pay for the electricity, power generators, and chillers.

[Blake Golliher]

... same power to run a 144 terabyte FC drive as a 750 terabyte ATA drive, so using the largest drives possible ...

Gigabyte, right?

[Alex Gorbachev]

Coming from the database workloads, I tend to count, first of all, the number of disk spindles and then capacity.
Blindly, going to 750G ATA drives in RAID 5 from 36G FC in RAID 1+0 just to save on power might be a disaster unless it's clear what are the performance requirements and whether the new storage infrastructure with 5 times higher capacity and 2 times less power consumption would be able to sustain the old workload.