Every night, I have SuperDuper! create an image of my hard drive to an external drive. This works great, and has saved me from system failures a number of times.

However, OS X is constantly treating it as if the installation of OS X on that external drive is a part of my actual system rather than just a backup on an external drive. To wit, when I do a Spotlight search all results are duplicated. (Even though I have expressly forbidden Spotlight's indexing of the /Volumes folder through System Preferences.) Every app in the Mac App Store, when updated, will update the copy on my system and then report again a second time that this app needs to be updated again, and running the update will update this external drive. Apps that request the location of my iPhoto library always list two.

How can I get OS X to just treat that drive like an external drive full of data, rather than as a part of the current OS X installation?

  • I'm going to give an answer you might not like. All the hacks I've seen to lock down the drive are more trouble than they are worth and seem prone to breaking at the wrong time.
    – bmike
    Commented Sep 18, 2013 at 21:12

1 Answer 1


Most people I know that keep bootable backups do one of two things:

  1. Do these backups far less often and use Time Machine to keep the most up to date backup.
  2. Script mounting and ejecting the drive as part of the copy process.

The first option works well for a monthly rotation (and just before major updates like an OS update or upgrade) since the bootable image is more about getting running rapidly than needing to have a perfect mirror of everything when your actual data is backed up elsewhere.

The second option I have seen for people that really despise Time Machine since you will get all sorts of unwanted confusion having two (or more) OS mounted at the same time with Spotlight, App Store Updates and worse mixing up which file should be opened or updated.

Assuming you have already told SuperDuper to not make a fresh copy and instead perform a smart update, you might be in the same boat as these:

The last topic about indexing may also help you if you script the mounting and unmounting as spotlight may want to reindex the drive each time depending on precisely how you have SuperDuper set up.

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