I Found an Easy Fix for my Recalcitrant Mac Backup Disk

Dr. Mac’s Rants & Raves
Episode #156


A couple of weeks ago my Mac displayed an alert telling me that my Time Machine disk was damaged and that I should repair or replace it as soon as possible. The first thing I tried was Disk Utility’s First Aid feature, which has been part of OS X since time immemorial. Sadly, it was unable to fix the damage and suggested I back up my files and erase the disk.

By the way, I’m pleased to report that Disk Utility in OS X 10.11 El Capitan no longer requires you to reboot from another disk in order to run First Aid on your boot disk—yet another reason you might want to consider upgrading to El Capitan if you haven’t already. 

Moving right along, I don’t give up easily, so I tried some third-party disk utilities (which shall remain nameless for reasons that will become apparent shortly), but none could repair the damaged disk.

I was about to throw in the towel and erase the disk, but there was one more thing I wanted try: a Safe Boot. To perform a Safe Boot, first shut down your Mac, wait 10 seconds, and then press the power button. Immediately after the startup tone, press down the Shift key and keep pressing it until you see the gray Apple logo and progress indicator. To reboot in normal mode, restart your Mac again without holding down any keys.

A Safe Boot does a bunch of behind-the-scenes magic. It verifies your startup disk and attempts to repair directory issues if needed. Then, it starts up using only required kernel extensions while preventing all non-Apple Startup and Login Items from opening automatically. Finally, it disables all user-installed fonts and deletes a bunch of system cache files.

I didn’t expect a Safe Boot to fix my damaged external disk, but I figured it was worth a shot before I gave up. Much to my surprise, when I ran Disk Utility’s First Aid after my Safe Boot, it reported that the disk was just peachy and required no repairs.

By the way, OS X 10.11 El Capitan doesn’t give as much feedback as previous versions; to determine if you’ve actually performed a Safe Boot, open the System Information application and click Software in the column on the left as shown here:

Is your boot safe? Only System Information knows…

The moral of the story is that you should try a Safe Boot anytime your Mac misbehaves, even if you don’t expect the Safe Boot to fix anything. This wasn’t the first time a Safe Boot fixed a problem that had stumped me otherwise and it won’t be the last. There’s no downside, so before you start tearing out your hair, give Safe Boot a try.

One last thing: If your iOS device misbehaves, try a reset/restart (similar to a Safe Boot) by pressing and holding the sleep/wake button and the Home button simultaneously, and then releasing them after Apple logo appears on the screen. Like a Safe Boot, there’s no downside to a reset/restart and you’ll be surprised at how often it resolves iDevice issues.

And that’s all he wrote…