I'm not big on saving electricity at all and I'm trying to decide whether to select Mac's “Put hard disks to sleep when possible.”

What are the pros and cons of doing so?

For example, can I expect the hardware to last longer by keeping the hard disks on 24/7 versus putting them to sleep?

I'm using MacBook Pro (2017) running Sierra (10.12), but question is also interested in other (future) versions.

And why is “…hard disks…” plural when there's only one?

  • Some folks say turning off that feature will solve the mysterious "Disk not ejected properly" error that plagues some of us with connected external SSDs for our Time Machine backups. Nov 19, 2023 at 7:56

3 Answers 3



  • on older traditional rotating disk drives it will save some power

  • on the same type of drive it often parks the heads making it less fragile in cases of unplanned moving/shock/drop


  • rotating hard disk drives will live shorter due to the fact that it’s the starting and stopping that kills them, not running idle

  • slower initial access to the disk as it starts after it was put in standby (it needs to spin up before it can be used)

None of this really matters to solid state disks as they are pure electronical devices with no mechanics. Their power use is directly proportional to disk activity. While they often do have extra low power modes, you won’t actually benefit much from it since it is not much less than its normal power regulation.

The reason this is plural is because it can also apply to external disks, and desktop macs used to have space for up to six harddisks. The 2009 Mac Pro has 4, for example.

  • Do you mean that if I only use SSDs, I should leave the setting on.. or off?
    – Pacerier
    Jan 25, 2018 at 18:21
  • 1
    If you only use SSDs it doesn’t matter what you set it to. I’d suggest leaving it off by default in case you connect external hard drives. Jan 25, 2018 at 21:53

I'm not a 100% professional with hard drives, but here is what I would think some of the disadvantages and advantages are.


  1. Like you said, an advantage is the disk life might be extended. Though this extra amount of life might not be that noticeable.
  2. Battery life - The hard drive obviously uses electricity to power it. If the hard drive is put to sleep it will turn off, thus not using any electricity which will help the battery last a bit longer.


  1. Longer wake time - When the computer goes to sleep the hard drive will completely stop, so when the time comes to wake the computer the hard drive will need to spin up. There will also be a delay whenever the hard drive needs to spin up after it's been put to sleep.

Hope this helps.

  • 1
    "Longer wake time" – If this is 'longer wake up time', how so? If it goes to sleep, everything is put to sleep? What difference is then there for the setting? Jan 22, 2018 at 22:11
  • @LangLangC chances are there will be some synchronization; the sleeping hard disk(s) will not be able to spin up concurrently with the rest of the system because the rest of the system depends on them. Therefore, the wake up time T will become S + T (T must wait for S) where S is the additional spin-up of the slept hard disks. Mar 6, 2023 at 12:40

You don't have to worry about that setting. Apple in their infinite wisdom have decided that it should have no effect. Whether you enable or disable it, it will put your disks to sleep. At least on High Sierra.

Why they've chosen to keep the setting around is anyone's guess. Maybe it's bug — these days that seems very likely ;)

EDIT: As for how I know this, it's based on me trying the setting out on High Sierra to prevent 10 attached USB drives from spinning down, and confirming that the setting does not have any effect.

  • 1
    Do you have a reference for any of what you are saying?
    – kojow7
    Dec 12, 2018 at 5:23
  • It might not have an effect on certain cases, but still kick in when needed. "10 attached USB drives" sound like a lot. The settings it not "NEVER put hard disks to sleep", but "Put hard disks to sleep when possible" e.g. whether to take advantage of more cases to put hard disks to sleep or not.
    – Hejazzman
    Nov 14, 2019 at 8:34

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