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I am currently backing up a large amount of files to a portable hard drive on my Macbook Pro running High Sierra.

It should take a few hours, and generally in around 15 minutes my laptop screen goes dark, and when I wake it, it asks me for my password again.

Does my computer continue to copy files when this occurs?

If so, does it do so at the same rate, or a reduced rate due to the computers state?

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There are various modes of sleep a Mac can go into. At this point your question only describes the fact your laptop screen goes to sleep, but this is different from your computer actually going to sleep.

Regardless of your settings and assuming your MacBook Pro has a continuous power source, then a system event such as copying a large amount of data will continue to occur even if various parts of your Mac go to sleep.1 This is because if your Mac is in the middle of an action such as copying files, it will not go entirely into sleep mode (e.g. your display may go to sleep, but your drives are still fully powered up for read/write purposes).

In terms of the speed at which data is transferred, this can be affected by a number of factors, but in your scenario the transfer rate should not be impacted.

Of course, if you're copying a large amount of data, it is recommended you have your MacBook Pro plugged into an AC power source.

For more information on your Mac's sleep capabilities, you may want to refer to the following content:


1 This answer assumes we're talking about a Mac scheduled to go to sleep as a result of its Energy Saver settings, and not because it's been manually put to sleep by the user (e.g. by closing the lid, etc).

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  • Is this a scenario that macOS's "Power Nap" feature covers?
    – Dai
    Oct 2 '17 at 5:55
  • But if you close the lid, the copy is probably interrupted? Closing the lid usually stops everything Oct 2 '17 at 6:47
  • @Dai No, PowerNap is a relatively newish feature in MacBook Pro models (only appearing in Retina models). While Power Nap allows your Mac to perform some activities while in sleep mode, a Mac has always been able to continue copying files if the process was started prior to when the Mac is scheduled to go to sleep, as this will prevent the scheduled sleep from taking place until later. For more info about Power Nap, refer to: How Power Nap works on your Mac.
    – Monomeeth
    Oct 2 '17 at 6:51
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    This answer is very confusingly written, almost to the point of wrong. You say that the Mac continues to copy files when it goes to sleep, but that is obviously incorrect. I believe what you're trying to say is that a Mac can blank the screen and continue to copy files. That's certainly true, but screen-blanking is not the same thing as "sleep". The terms have never been synonymous. Sleep refers to a low-power suspend mode affecting the entire system.
    – Cody Gray
    Oct 2 '17 at 10:50
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    The comment "a Mac has always been able to continue copying files if the process was started prior to the Mac putting itself to sleep" is especially wrong. If the Mac puts itself to sleep, it won't continue copying files. What actually happens is that the ongoing file copying prevents the system from putting itself to sleep. Your phrasing makes it sound like something very different is happening.
    – Cody Gray
    Oct 2 '17 at 10:53
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A little trick if you want to momentally keep an eye on your transfer:

$ caffeinate -t 3600 &

This command line keep your computer awake for an hour.

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