How to stop a Mac’s hard drives from spinning down

Hard disk drives (HDDs) work by spinning their internal platters. Only during rotation can data be read or written. It’s been decades since they were able to stay online, but No spins in standby mode. This reduces power and can also reduce wear caused by heat and mechanical use.

macOS automatically sends a signal to internal hard drives (on older Macs) and external ones that tell them to stop spinning after a period of not accessing the data stored on them. The next time the hard drive is needed, there will be a slight delay while the drive reaches the required speed. Some people have an intermittent but constant need to use their hard drive and find that the constant short lags add up, and they are rightly concerned that the frequent spinning up and down leads to its own set of wear-out problems.

Apple provides a convenient way to control this behavior in System Settings with the “Hibernate hard drives when possible” setting:

• On a Mac laptop, go to System Settings > Battery and press Options. You can select Always (the default) and three options: Battery Only, Power Adapter Only, or Never. Battery or power adapter only puts the drive into sleep mode whenever possible, with only the power source that may remain desired. Will never do what it says: macOS never tries to shut down the drive.
• On your Mac desktop, go to System Settings > Energy. There you can enable or disable this setting as desktop Macs require a power adapter.

Some hard drives and some macOS installations may ignore this setting and continue to stop the hard drive after a short period of time. If you find this inappropriate, you can open Applications > Utilities > Terminal and enter the following command followed by Return; Enter the administrative password when prompted:

sudo pmset -a disksleep 0

0 means “never”, but you can set it to a higher value in minutes, for example 30 means “30 minutes”.

You can’t enter a command line command to reset the hard drive sleep duration to the default, which is 10 minutes on the unmodified Mac desktop I tested on.

This article about the Mac 911 is in response to a question submitted by Macworld reader Howard.

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