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My MBP Retina 13″ late 2012 is showing the stop sign and I know that I need to reinstall my OS. I have not got my hard drive backed up with Time Machine. Is there a way in which I can backup my hard drive to an external drive using Disk Utility and then restore it back once I have reinstalled the OS (I have to restore as for some reason I don't have enough space or something)?

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Absolutely - this is a good plan in general - having a bootable backup in addition to a Time Machine interval backup.

I like to get a SD card / micro SD card and install an emergency boot OS with just enough tools to fix any situation.

I would do that before making any changes. Next, you will want to measure how large your drive is - open Apple Menu - about this Mac and look in storage:

enter image description here

For this Mac, you would need 185 GB of space.

  1. Connect a USB drive and partition it to have one free partition that's at least 5 GB larger than the space needed. (I would go 15GB or more larger if you care about speed or ever booting from that partition)
  2. Erase the partition you will be using and format it as OS X Extended and name it "target" or something unmistakable.
  3. Shut down the Mac and hold R when booting to boot to Recovery HD
  4. Use Disk Utility from Recovery to restore data from Macintosh HD to target
  5. Wait - enjoy some tea or coffee or whatever
  6. When things are done, power off and boot holding option - you should see two boot drives with different icons on the grey screen and can test booting from the clone.
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    Caveat: If the original is not bootable, there is a pretty good chance that the target disk isn't bootable either. Additionally I miss a hint that the OP shouldn't restore (restore as in Disk Utility -> restore image) the "backup" but migrate chosen content of the target back to the reinstalled OS X. If the target is bootable then less time consuming tasks like repairing the main volume instead of backing up the original and re-installing OS X should suffice. – klanomath Aug 22 '15 at 16:04
  • @klanomath You rock - I will add a part about making a bootable emergency disk too. – bmike Aug 22 '15 at 16:04

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