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I've got a mid-2013 11" MacBook Air that I fixed up.

It had no SSD when I got it but I've been running it off an external USB 3 hard drive fine for about a year and a half including backpacking around the world for a year.

But in the last few weeks the whole OS has been prone to crashing. Sometimes after a couple of days uptime, sometimes after only a short time.

I'm trying to narrow it down to a bad motherboard or bad hard drive.

Normally I wouldn't expect a bad hard drive to crash the whole system but just report various errors and warnings from the OS. Or if it were to cause a crash I would expect the OS to detect it most of the time and display some kind of dialog on the screen before restarting.

Often though it seems to crash when I'm moving the computer or the external drive or touch the cable. Most of the time moving it does not cause a crash though.

I have tried both USB ports so I can rule out damaged ports. It could be something to do with the cable or the drive though.

But if anyone can tell me for 100% sure that a bad hard drive or cable is ever known to crash the whole OS I can try to find another drive to test.

Likewise if anyone can tell me for 100% that a bad hard drive can never crash the whole OS I can focus my attention elsewhere.

Extra info:

Once or twice after a crash it restarted with the flashing folder icon but started up fine next time. I never got any errors about the hard drive from the OS or any app. Checking the drive with the OS tools finds no errors. The drive has both Mac and Windows partitions and I've tested on both OSes. I haven't yet seen any problem using the drive on my Windows laptop but I mostly use the Mac now.

The only causal factor I can think of is that one day I put the Mac in my backpack with the external drive still attached. The Mac will sleep but not hibernate due to the OS design. I was jogging for an hour or two and when I opened my backpack the drive cable was no longer plugged in. Plugging or unplugging a USB device wakes a sleeping Mac and waking the Mac will cause the hard drive to start. Bumping or shaking a running hard drive can damage it. None of this should've had any effect on the rest of the Mac hardware I can think of.

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It's not really clear what you mean by completely crash or crash the whole OS, but yes a bad hard drive can cause a crash/freeze.

In your case there's a few things you can still try:

  • Try a new cable
  • Reset the NVRAM
  • Try booting into Safe Mode

Obviously I don't need to explain how to try a new cable, so I've included steps below for resting the NVRAM and booting into Safe Mode.

Resetting the NVRAM

Follow these steps:

  1. Shut down your machine. Yes, a full shut down, not just logging out.
  2. Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
  3. Hold those keys down until your Mac reboots again (i.e. a 2nd time) and you here the startup chime.
  4. Let go of the keys and let your Mac reboot normally.

Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

Boot into Safe Mode

Follow these steps to boot your Mac into Safe Mode:

  1. Fully shut down your Mac
  2. Restart your Mac
  3. Immediately press the Shift key and keep it down
  4. Let go of the Shift key when you see the login window (NOTE: If you have FileVault enabled you may need to log in twice).
  5. Take a note of what happens (i.e. could you boot your Mac okay, does it still crash?)
  6. Exit Safe Mode by restarting your Mac as normal
  7. Test your Mac again to see if it still crashes

Once you've booted into Safe Mode, let me know how you went and we'll go from there.

If by any chance you find your Mac doesn't crash while in Safe Mode, but it does crash when booted normally again, then we know the problem is basically software related and we can troubleshoot that further.

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Your internal hard drive is likely failing.

The Disk Utility will not reveal a failing hard drive, S.M.A.R.T. does that.

DriveDx is a great tool to check S.M.A.R.T. status of your drive. (https://binaryfruit.com/)

I would advise to backup your data as soon as you can.

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  • The computer has no internal hard drive. It also hasn't got any worse in the 11 months since it started happening.
    – hippietrail
    Commented Oct 16, 2018 at 23:12
  • "Normally I wouldn't expect a bad hard drive to crash the whole system". I find you overly optimistic! :)
    – brunobhr
    Commented Aug 6, 2019 at 21:36

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