What needs more power: hard drives or SSDs?

A hard drive’s motor needs a lot of energy to keep it rotating. SSDs, on the other hand, contain no mechanical components, which is why they are considered to be more energy efficient. Storage services provider Scality is now claiming that a hard drive is not necessarily more power hungry than an SSD – it depends on the application. The company’s example calculations are based on information from the data sheets of individual drives and on assumptions about the distribution of reading, writing and doing nothing.

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However, Pure Storage, a provider of all-flash systems, predicted a few months ago that hard drives would become extinct in the near future because they would consume too much energy.

Both assumptions apply primarily to the use of hard drives and SSDs in data centers and have little to do with the power requirements of an office PC. We measured it a few years ago as part of a focus on IT myths. The following paragraphs have not lost their validity to this day, but they do not provide any information about the whereabouts of hard drives in server cabinets.

Question: Are SSDs more economical than hard drives?

Yes, that’s right. For this test, we used the Asrock DeskMini 110 (a current mini PC at the time), equipped with the 250 GB Samsung SSD 750 Evo and with a 2.5-inch hard drive from Western Digital (WD Blue). The SSD system required 14.9 Wh in one hour, and the required energy increased by 2 Wh when equipped with a hard drive. PCMark 10 Basic ran for around 25 minutes, the rest of the time the system ran idle (Windows 10).

A 2.5-inch hard drive actually requires little more power to operate than an SSD. The higher energy requirement is based on two factors: On the one hand, the hard disk needs much longer for the IO tasks than the SSD, so it needs more energy. On the other hand, after a few seconds of inactivity, SSDs switch to an energy-saving mode via the SATA link power management, in which they consume a maximum of a few hundred milliwatts. Hard disks also take into account link power management, but this hardly reduces their power consumption; the WD Blue HDD still consumes just under one watt.

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You can use the advanced settings in the energy options to specify that the hard disk should also switch off its motor; this reduces the input power of a 2.5-inch disk to around 400 milliwatts. In the test system, we set the switch-off time to a practical five minutes, but a hard drive still needs significantly more energy than an SSD, even when idle. 3.5-inch hard drives are even more power-hungry than their smaller relatives, which further widens the gap between an SSD and a hard drive system. (ll)

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