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So, I completely understand the value of putting a hard disk (specifically) to sleep in some cases especially in the pre-SSD days of the past. It can save power, lower noise and such. But in the case of modern systems that are increasingly SSD-based, does this option have any value at all?

My MacBook Air (2018) running Mojave (10.14.1) has “Put hard disks to sleep when possible.” checked off by default (in System Preferences > Energy Saver), but this system uses an SSD.

Is this option only focused on hard disk drives and ignored by SSD drives?

I can’t imagine the internal SSD would ever “sleep” but correct me if I am wrong.

In short, does the “Put hard disks to sleep when possible” option have any affect on SSD drives in macOS?

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10

According to Apple:

Put hard disks to sleep when possible

This setting powers down the hard drive motor when you aren't reading or writing files from the drive. Solid-state drives (SSDs) don’t have moving parts, so this setting doesn’t affect Mac computers that use only SSDs to store data.

Consider deselecting this option if you have an internal or external non-SSD drive and you use apps—for example, pro audio or video editing software—that work better with continued read and write access to the hard disk.

Source: Apple: Use the Energy Saver settings on your Mac [Bold emphasis mine]

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Solid-state drives (SSD) do not use a motorized mechanism to read or write data. For Mac computers that only include a built-in solid-state drive, this setting does not affect the built-in drive. It only applies to externally connected, mechanical drives.

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SSD vs HDD uses about 50% less of energy, so having the option turned on will help reduce overall power consumption.

ie - my MBP 15" 2011 has 95 Wh battery in it (when new, down to about 60-70 now), so in a hour with the option you will save some 1-2% of battery life with the option on, depending on use.

https://therevisionist.org/reviews/ssd-vs-hdd-power-consumption/ https://linustechtips.com/main/topic/950687-hdd-vs-ssd-temps-power-consumption/

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  • That power consumption comparison should be of "in use" state, not idle. – ankii Dec 26 '19 at 12:39
  • Yes, but idle is also not null. There are plenty of resources online that list anywhere from 30-50% power reduction for the SSD, but in my view that is still significant. – mrmut Dec 26 '19 at 12:41
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    Please reread the question. It's not about comparing HDD vs SSD, it's about the effect of a power-saving option on SSDs. – nohillside Dec 26 '19 at 16:48

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