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I am planning to install a second OS X on an external HDD, I was wondering when I boot in external HDD will it in any ways affect my first OS X installation? Will it have the permissions to write or read from it? Or will spotlight start to index that HDD? If yes how can I isolate my first installation from being affected? (without using "third-party apps" or "file vault")

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up vote 2 down vote accepted

The disk which you don't boot on will show as an external drive to your current OS HD. You'll have full read/write accesss, Spotlight will start indexing it.

To prevent Spotlight from indexing your second drive, open a Terminal window and type: sudo mdutil -i off /Volumes/2NDDRIVENAME

and replace "2NDDRIVENAME" by the name of the disk you want to exclude. Beware if you have a space in the drive name, you may need to use the "\" escape character:

sudo mdutil -i off /Volumes/MacHD

sudo mdutil -i off /Volumes/Macintosh\ HD

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Is it possible to isolate the other drive from new installation? – 2TCG Feb 28 '13 at 17:31
you mean, make the other drive invisible while you install your 2nd system ? Yes, go to the Utilities menu when you've booted on the OSX install volume, open Disk Utility, select the volume you want to hide and click on the "unmount" button. Quit Disk Utility, the Installer will only see one volume. – PEM8000 Mar 1 '13 at 9:37
You mean it won't detect that volume after installation? – 2TCG Mar 1 '13 at 11:52
my previous comment just works during the time of the installation. When your Mac boots on the new system on the new drive it will see the 2nd physical hard drive and automatically mount its partition. – PEM8000 Mar 1 '13 at 13:59
If you want to prevent your second volume to show, you will need to create the file /etc/fstab and specify the ID of the volume to ignore (see example on ) – PEM8000 Mar 1 '13 at 14:01

Try this

It was working for me... (WD 2TB External hdd)

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