Do hard drives use a lot of electricity?

Individually, no. One drive sipping a few watts costs very little a year. The cost only becomes noticeable when you run a lot of drives at once, which is exactly why fewer big drives is cheaper to run than many small ones.

Do bigger hard drives use more power?

Barely. A large drive uses roughly the same few watts as a small one, but stores far more data. So per terabyte, big drives are actually more power efficient, another reason to buy big.

How Much Power Does a Hard Drive Use?

Q: How much power does a hard drive use?

A typical 3.5 inch desktop or NAS hard drive draws only a few watts idle and a little more when actively reading or writing. Over a year of constant running that is a modest cost per drive, but it adds up fast across many drives.

Published: July 25, 2026

Live comparison · Amazon.com

Pulling live prices…

📊 As of August 15, 2026, SATA HDD (8TB+) averages $46/TB vs $41.58/TB for SAS HDD (8TB+) on Amazon.com — SAS HDD (8TB+) is about 10% cheaper per TB.

Sourced from real discussions on r/homelab and r/DataHoarder, cross-checked against live PricePerGig listings.

A single hard drive uses 9 watts when spinning all day long. A hard drive also uses just over double the energy just to get spinning up in the first place, but that’s usually rare or not worth calculating; until you have 20 or more of them, then you’re going to want to stagger the startup of each one or end up in a continuous boot up/run out of power merry go round.

Thinking about the power something uses is usually pretty far down on the list, if at all, but when you consider leaving something running 24/7 like a NAS, combined with file systems like ZFS which by design need every disk in the pool spinning to access any data at all, then you start to at least do a quick sum.

Another aspect to multiple drives is the hardware to connect to them; not just the power supply lines, but actual SATA or SAS connectors, even driving those takes up power, a surprising amount. When you really start looking at getting a large amount of storage, you’ll come across SAS as an alternative to SATA. Many enterprise drives use SAS and they end up being a little cheaper per TB too. However, and you probably saw this coming, you don’t have any SAS connectors on your motherboard. One of the most common ‘starter’ SAS connectors is a PCIe card - LSI 9201-16e are popular, that one PCIe is popular because it’s pretty cheap at around £30 on ebay; but it also uses 37 watts of power, even when idle, doing ‘nothing’. That’s 4 drives worth of power burning just to connect to 4, 8 or 16 drives!

The table above compares the live price per TB for SATA and SAS hard drives of 8TB and up on your marketplace, so you can see for yourself whether the cheaper SAS drives are worth the card you have to power to reach them.

What a hard drive actually draws

Let me give you real ballpark figures.

A typical 3.5 inch desktop or NAS drive draws only a few watts when idle, and a little more, still single digits, when actively reading or writing. Around 9 watts spinning all day is a fair working figure, and spinning up from cold costs just over double that for a moment.

Spinning all day, every day, that works out to a fairly small cost per drive over a year. Noticeable, but hardly scary.

So one or two drives running constantly is pocket change. The picture changes when the drive count climbs.

Why drive count is the real cost

Here is where running cost meets buying strategy.

Every drive you add is another few watts, all day, every day, forever.

Run forty small drives and you have a permanent low level heater humming away, quietly eating power and money. Run six big drives for the same capacity and you sip a fraction of the electricity.

So the wall of small drives is not just worse value to buy and more failure points. It is also more expensive to run, month after month.

The connectors draw power too

Here is the cost people forget entirely: the hardware that connects the drives.

Your motherboard gives you a handful of SATA ports and no SAS ports at all. Once you are past those, you add a host bus adapter, and that card draws power all on its own, all day, whether the drives are busy or idle.

How much depends enormously on which card you buy, and the gap is far wider than people expect. A small 8 port card is fairly modest. A 16 port card like the 9201-16e, or a RAID class controller with onboard cache, is in a different league entirely, and the cheap ones on eBay are very often exactly those big ex enterprise cards.

At the top end that is several drives’ worth of power, burning away just for the privilege of connecting more drives, and it never spins down because there is nothing to spin down.

So price the card into the sum, not just the disks. The table above compares SATA against SAS on price per TB, and if the SAS saving is thinner than the card costs you to run, the plain SATA drives win outright.

It is not a reason to avoid SAS, and used enterprise SAS drives are often excellent value per TB. It is just a reminder that the drive count is not the only line in the sum.

Buy one already flashed to IT mode

One thing worth knowing before you click buy. If you’re buying a cheap LSI PCI adapter to get more connectors than what your motherboard has, you’ll want to buy one that’s already flashed to ‘IT’ mode, or do that yourself.

IT mode turns the card into a plain pass through, so the operating system sees each raw disk exactly as it is. That is what ZFS, unRAID and every other software array actually want. Left in its factory RAID mode, the card insists on owning the disks itself and hides the drive from the very thing you bought it for, SMART data included.

Here is the link with all the info on that, and it is the guide worth following rather than a random forum post, because a bad flash can leave the card unusable.

Big drives are more efficient per TB

This is the part people miss, and it is lovely.

A 20TB drive uses roughly the same few watts as a 4TB drive. Same motor, same spin, vastly more storage.

So per terabyte stored, the big drive is far more power efficient. You get more data for the same trickle of electricity.

Glance at the live price per TB table above. Big drives win on purchase price per TB, and they quietly win on running cost per TB too. The value stacks up twice.

How to keep running costs down

A few easy wins.

Buy big, few drives, using the best price per TB on the live table above.
Let drives spin down when idle if your setup allows, though always on is fine for NAS use.
Do not buy a wall of tiny drives. It costs more to buy and more to run.

Simple, dense, efficient. That is the whole trick.

The bottom line

A hard drive uses only a few watts, so one or two cost almost nothing to run. The expense comes from running many drives at once.

Fewer big drives is cheaper to buy, cheaper to run, and more power efficient per terabyte. Check the live price per TB above, buy big, and your storage stays kind to both your wallet and your electricity bill.

So you came here for price per gig, and we’re talking about watts per gig! But running your own home NAS - or data centre, well, it ends up being factored in. It’s a shame, I believe energy and water should be ‘free’ as possible, imagine the innovation that would take place, but here we are, so you’ll want to look for larger and less to save the energy, and generally use up less hardware.