Feature: How to cut energy costs at the node

An underlying issue in the FM versus IT debate specifically concerns the level at which data centre power usage is measured and monitored.

“It’s easy to get an understanding of power usage at the facility level, but customers now want to understand it at the IT level,” claims Mark Roberts, business development manager for IT at Rittal.

Roberts divides the data centre power load in two – a perspective he calls the ‘two sides of the house’.

On one side, the facility load is powering airconditioning, chillers, uninterruptible power supply (UPS), power distribution units (PDUs) and so on, while on the other side the IT load draws power for servers, networking equipment and storage.

“You obviously need to monitor both sides,” explained Roberts.

“Traditionally most people have monitored power distribution high up at the facility level, but now they want to monitor closer to the actual piece of IT equipment, which means monitoring at the socket level.”

Socket-level (also referred to as node- or equipment-level) monitoring is this year’s hot button topic in power management.

“Taking measurement down to the socket level is a major step forward for organisations from a visibility standpoint,” said Raritan’s Gary Hull.

“Measuring by node or infrastructure device means customers now have a benchmark to gauge power usage and can work towards reducing consumption and costs from the baseline they’ve established.

“It helps them understand what devices are consuming power, how much are they consuming and is it necessary for them to consume that much,” explained Hull.

Hull said Raritan had seen a strong understanding demonstrated by local data centre operators of the need for node-level monitoring and measurement.

That comprehension had already translated into sales into the Department of Treasury and Finance and JP Morgan, among others, he said.

Ciaran Bolton, product manager for data centre solutions at Eaton, is also focused on socket-level opportunities.

“It’s really coming right down to the node level as IT managers want to get as granular as possible,” Bolton said.

“We’re getting to the point where the cost of energy is almost the largest single cost in building or running a data centre.

“If you can meter and monitor down to the node level, you can identify and consolidate volume servers running at 10 or 15 percent utilisation to stop wasting that energy and save some money,” Bolton said.

Who nodes?

To understand why socket-level measurement is so important is to take lessons in the disparate worlds of rough calculation and thermodynamics.

According to Rittal’s Mark Roberts, IT managers typically work out how much power they’re using at a socket level by adding up the plate ratings listed on the back of each piece of equipment.

They then subtract this total from the room’s known capacity to work out the power window they have left.

“The plate rating is usually the worst case scenario – the true working scenario is a lot less,” explained Roberts.

“For example, if the rating says the box draws five amps it’s probably only drawing around 2.5 or 2.75 amps in reality.”

Roberts said he routinely applied what he calls a ‘diversity factor’ of 0.6 to listed plate ratings for this reason.

However, measurement can (and in the current environment, probably should) be a more exact science.

“If people have a way to dynamically measure power, they can see exactly how much each box is drawing,” said Roberts.

Gaining a better understanding of the socket-level power draw can result in exponential savings at the facility level. Emerson refers to this as the cascade effect.

Put simply, the cascade effect says that every one watt of savings made at the server component level (processor, memory, hard disk etc.) creates a reduction in facility energy consumption of approximately 2.84 watts. (i.e. a one-watt reduction in IT load plus a 1.84-watt reduction in the facility load).

“When you take a single kilowatt off the grid and into the data centre you get losses all the way through [to the IT equipment],” said Spiteri.

He added: “Around half the power that comes in is used to power and cool the building as opposed to power the IT equipment. Right upfront only half the power you buy is going into the whole reason that the building exists.”

This is the key to selling socket-layer measurement – it helps gain a better understanding firstly of how much power each box is drawing on and secondly how this affects the total power consumption of the centre.

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