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19 Apr 2022

Power considerations of a home NAS

The unit cost of electricity has risen significantly in the last few months and is expected to remain high for the foreseeable future. This is an opportunity to review your energy usage. The annual cost of powering devices that are continuously powered can be high. We use a NAS device as an example, but you should review all devices that are continuously powered.

A home NAS (Network Attached Storage) is a staple for computer enthusiasts, no home lab is complete without one. However, as energy prices continue to rise globally, we thought it would be the perfect time to analyse how much a home NAS actually costs to run, and more importantly, steps that you can take to reduce it. Before reading about NAS power consumption, I recommend reading this post that explains how Hard Disk Drives (HDDs) work, as they are currently the main storage device used by a NAS.

First, let’s look at how much energy a home NAS uses. In this example, we are assuming that the NAS will have 100% uptime for a year; assumption number two is that the NAS will use the same amount of energy consistently. We have used the April 2022 energy cap for UK electricity which, for most people, is what they are now paying per unit. You should consult your electricity provider for what you are being charged.

Days on per year365Days
Hours on per day24Hours
Annual Time On8760Hours
Cost of energy0.28 (0.37)£ (US$)

The table below shows the annual cost of running a 35W NAS:

Power consumption35Watts
Annual Energy Consumed306.6kWh per year
Annual Cost86 (113)£ (US$) per year

Increasing the power to 40W shows that even a slight increase in power consumption can have quite a drastic effect on the annual cost:

Power consumption40Watts
Annual Energy Consumed350.4kWh per year
Annual Cost98 (129)£ (US$) per year

What can I do to reduce the cost of running the NAS?

This is a good question. As we can see from the data above, there are three ways to reduce the annual cost of running the NAS. Number one, reduce the ‘cost of energy’; unfortunately, this is not looking likely recently as the cost of energy continues to increase. Number two, reduce the ‘annual time on’ of the NAS. Number three, reduce the ‘power consumption’ of the NAS.

Reducing the ‘annual time on’ of the NAS

Since reducing the cost of energy is not looking likely, and also not something that we as individuals can control, we will move on to option two. Reducing the ‘annual time on’ of the NAS is the easiest way to reduce the annual cost of running the NAS. However, it is important to also take drive spin down and spin up into account. The peak power consumption of a HDD usually occurs when the drive is spinning up, even though turning the NAS off will reduce the amount of power that the NAS uses over time, it is important to note that when the drives spin back up, they will temporarily use more power until the HDDs reach their running speed, at which point the power usage will be mostly consistent. Spin down/up also puts more strain on the drive and may shorten the drive’s lifespan. It is recommended that the disk manufacturer’s documentation is checked for the start/stop count of the HDD. 

Reducing the ‘power consumption’ of the NAS

The next way to reduce the annual cost of running a home NAS is to reduce the power consumption of the NAS.

Swapping the HDDs in a NAS for Solid State Drives (SSDs) will reduce the amount of power that the NAS requires. However, SSDs are more expensive per gigabyte than their HDD counterparts. This can make the costs exorbitant for large amounts of data. If SSDs are unsuitable for your home NAS, then further consideration can be taken when selecting a HDD. 2.5 inch HDDs require less power than their 3.5 inch counterparts, and are more resilient to spin up/down. This makes 2.5 inch HDDs a good choice when the NAS is frequently powered down, or powering saving options like drive spin down are enabled. SSDs can also be implemented as a cache in the NAS, enabling the HDD to spin down for longer periods of time, as data that is accessed frequently can be retrieved from the cache. A read-write cache also allows data to be synchronously written from the cache to the HDDs reducing the time it takes to write data to the HDD.The RPM of a HDD will also directly affect the amount of power that the drive requires. The higher the RPM of the HDD, the more power that it will require. However, reducing the RPM of the drive will increase seek time and reduce I/O performance. It is important to note that I/O performance is less important for a NAS disk than for a local/system disk. In a home environment, you may find that the transfer rate is bottlenecked by the network, especially if WiFi is being used.

You may also want to consider the gases contained within the HDD. Conventional HDDs are filled with air (a mixture of oxygen, nitrogen, and a small amount of carbon dioxide and argon). Air is an important part of a HDD, as the read/write head “rides” on a thin layer of air, preventing it from coming into contact with the platter and causing a head crash, this is known as air bearing. Unfortunately, due to the speed that the platter spins at (usually 5,400 RPM and up), this air causes a considerable amount of drag, meaning that more energy is required to make the disk spin at the desired speed. Changing this air for a gas with a lower gas density like helium can reduce the amount of drag on the HDDs, and thus reduce the amount of energy that is required to spin the disk.

Reducing the number of disks that are stored in the NAS and replacing the disks with larger capacity disks will also reduce the power consumption of the NAS. It is important to note that the more platters a HDD has the more power it will require, this means that the number of platters should be noted when you are replacing several HDDs with fewer high capacity HDDs. Reducing the number of disks in the NAS may also remove the ability to provide fault tolerance through RAID configurations like RAID 1. This can be offset by performing a backup of the data stored on the NAS. Using Macrium Reflect, files on the NAS can be backed up over the network using a file and folder backup. You can read more about file and folder backups in this knowledgebase article. This blog post contains more information about the differences between RAID and backups.

So far, we have only looked at the effect of HDDs on the power consumption of the NAS. It is also important to consider the other hardware components and their effect on power consumption. Both the amount and speed of the memory in the NAS, and the CPU in the NAS will affect the power consumption. Obviously, adding more memory will require power to run; however, increasing the amount of memory can reduce the amount that the disk is accessed. The CPU that the NAS is using will also affect the power consumption, many NAS devices now make use of reduced instruction set command computer (RISC) CPUs like ARM CPUs. These CPUs have a lower power consumption than their x86-64 counterparts, and can be a good choice for a NAS CPU.

Other factors that do not directly relate to the NAS should also be considered, for example, if a network switch is required to connect the NAS to the network, then this will require additional power. It is also important to note that power supply efficiency will also affect the amount of power draw of the device. The more efficient a power supply is, the higher percentage of power drawn from the mains will be delivered to the components, the remaining energy will be lost as waste energy like heat. For example a power supply with an efficiency rating of 50% will need to draw 100W from the mains to deliver 50W to the connected components. I recommend reading this excellent article from Tom’s Hardware for more information about picking the right power supply for you.

A plug in energy monitor is a good investment. It will allow you to evaluate the actual power consumption of devices you already own. Remember that most devices will have a variable power consumption so it is best to measure accumulated power consumption over 24 hours. Don’t worry about the power factor, domestic power metres only measure the real power component.


In summation, over the course of the year, even small changes in wattage can add up. With rising global electricity prices, now might be the perfect time to assess your power consumption and make small changes to save big over the course of the year. When purchasing or building a device that will be powered consistently, it is important to be aware of the power usage of our devices, and where possible, make choices to reduce power consumption.