I am trying to dual boot OSX El Capitan and CentOS 7. Prior to attempting to install CentOS I'd like to create a clone of El Capitan on a partition of the same G Drive that I use for Time Machine.

I have created a second partition on the G Drive that is the same size as the the partition containing Macintosh HD on the MacBook Pro using Disk Utility. I formatted the partition using the Disk Utility Erase button twice, once using an Apple format, and once using FAT. I then tried to use Disk Utility Restore to clone the Macintosh HD to the partition. Both times I got the same error message "Source volume is read-write and can't be unmounted, so it can't be block copied".

How do I work around this?

I've tried following the instructions Apple.

Do I need to boot using Command "R" as this YouTube video suggests or is there another way?

  • 1
    What's a "G Drive" in a Mac context? Macs don't use lettered partitions. The best way to do it, btw is Carbon Copy Cloner [but software recs don't make good answers on SU] btw, Macs are only bootable from GUID/HFS, not MBR/anything. – Tetsujin May 22 '18 at 16:14
  • @Tetsujin G Drive is a particular manufacturer of external hard drives that work with Mac g-technology.com/products/outlet/g-drive-usb-silver#0G02529. – pacmaninbw May 22 '18 at 16:18
  • AH, OK - I hadn't heard of them - & their web page is a bit of a cookie-fest so I didn't read through it; but assuming 'regular' external USB drive, GUID/HFS+ & CCC will do it. It will even copy the Recovery Partition if you allow it when asked. Test the result before making any other changes, but I've never known it fail. – Tetsujin May 22 '18 at 17:03

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Browse other questions tagged or ask your own question.