Green storage: Savings to be made but tricky to achieve

UK energy prices have doubled since 2019

Energy prices have never been more unstable, with cost on an upward trend. If not managed closely, storage can eat up electricity to power hardware and keep it cool, and take up less-than-optimal areas of physical space.

Around 3% of all electricity globally is used by datacentres. And in the UK, electricity costs have doubled in the past three years.

Take a datacentre with 32 racks and electricity consumption of 10kW per rack, for example. That makes 320kW in total.

In 2019, a UK datacentre of that size would have paid about £280,000 a year (at 10p per kWh). By the end of 2022, that figure was more like £588,000 per annum (at 21p per kWh).

And that is with the government’s energy price cap for business in place, which is set to be lifted and replaced with a less generous discount from March 2023.  

Flash can reduce bills, but newer HDDs are probably a better bet

One area where IT departments can possibly make savings is in upgrading hardware to more efficient products. In particular, suppliers point to hard disk drives (HDDs) and their poor energy efficiency compared with solid-state drives (SSDs).

And it is true that spinning disk – with its moving parts – often draws more power than flash in all states of operation. HDDs draw several watts during reads and writes, and not much less when idle. Flash’s working power draw is often similar, but only a couple of watts when idle.

But if we look at a hypothetical configuration of half a petabyte’s (PB) worth of drives, the picture is not straightforwardly “flash good: HDD bad”. It really depends on the drives deployed.

As a starting point, let’s take Backblaze’s most deployed hard drive in 2019, a Seagate Exos nearline HDD (about £400 each back then) with random read/write power usage of 6-10W and idle of 5W.

If you wanted 500TB (terabytes) of usable capacity with those drives, you’d need 42 drives for the raw capacity plus an overhead for the RAID configuration. With RAID 5, that would total about 588TB, and so 49 drives, which at idle would consume 2.15kW for the year. At today’s UK electricity prices for business, that would cost £450.

That’s excluding storage controller and enclosure costs, of course, and running actual read/write loads would push up the wattage drawn, but for the sake of a baseline we’ll stick to idling.

Contemporary solid state

Compare that with 588TB worth of some more contemporary solid state. Here, with Seagate Nytro SSDs of 3.84TB capacity (153 of them, at about £725 each) and an idle power draw of 2W, the bill for the year would be £562.

But if you bump up SSD capacity, savings start to appear. With 38 WD Ultrastar 15.36TB SSDs (near £5,000 each) the electricity bill would be £419 (with an idle power draw of 6W, but a monstrous max usage draw of 18W).

That’s not much of an energy saving, but it does provide slightly denser storage.

In fact, newer, higher-capacity HDDs provide better energy savings, and cost much less per drive. So, going up in capacity even further, and with superior energy efficiency figures posted by the manufacturer, 27 units of 22TB WD Gold HDDs running at 5.7W idle (and random read/write of about 7W) would use £283 of electricity for the year (and cost £600 each).

Having said all that, if you last deployed storage hardware several years ago, moving to contemporary arrays or hyper-converged infrastructure will undoubtedly bring down energy bills and reduce physical space requirements.

Cloud viable for limited use cases

The argument that offloading data to the cloud, so that large providers take the strain of energy costs while benefitting from economies of scale, is a persuasive one – but the cloud does not necessarily work out less costly than on-site storage and IT provision. With gigabyte for gigabyte, it’s quite the opposite, in fact.

We’ve seen that 500TB of on-premise storage capacity (plus RAID overhead) will cost a few hundred pounds a year in electricity costs.

What does putting 500TB in the cloud cost?  If you put half a petabyte of data into AWS S3’s standard tier, the bill would come to around £114,000 per annum. Pricey.

But assuming that 95% of the data could go in the infrequent access tier, the cost comes down a fair chunk to just over half that, at £67,000. And if you put that 95% in the archive instant access tier, the bill comes down to £29,000.

That’s a lot more than 23 22TB HDDs would cost you for the year: say £283 of electricity plus £5,400 as one year’s share of three years’ outlay on the drives themselves.

Of course, none of that includes the building or staffing costs you’d incur on site, or the aforementioned storage array and controller costs. But then the cloud costs don’t include AWS’s monitoring and automation charges, or its per PUT, GET, etc charges. And we’ve only looked at S3 object storage. Block and file in the cloud cost a lot more.

Therefore, unless you’re talking about very limited – for example, a few terabytes – production workloads and for relatively short durations, or for large volumes of secondary data at very low “cold” storage rates, the cloud doesn’t look like a straightforward competitor to on-premise.  

As-a-service and consumption model options

Storage procurement has been disrupted in recent years by the introduction of as-a-service and consumption models of procurement.

Here, storage suppliers offer their hardware in a range of options that go from outright purchase with technology refreshes on a subscription basis, through to “as a service”, where the equipment is the property of the supplier and upgrades come as required, and perhaps predicted by artificial intelligence and machine learning-driven monitoring and telemetry.

At the as-a-service end of things especially, these offerings can help energy efficiency by providing the ability to flex capacity and performance up and down as required, based on service-level agreements.

Where this helps with energy efficiency is in the ability to right-size infrastructure to your needs, or to take advantage of modular storage hardware upgrades.

It used to be that when you needed more capacity or controller processing power there was little choice except to replace the entire array. Now, though, some suppliers can swap out individual components non-disruptively.