I partitioned my volume as MBR and was able to install Windows 7 + Mac OS X. Unfortunately, Disk Utility in Mac OS X cannot resize the Mac partition now because it's not a GPT volume. I also cannot upgrade to Mountain Lion because it requires a GPT volume. How can I safely convert the volume to GPT without data loss so that I can resize my volumes?
migrated from stackoverflow.com Oct 29 '12 at 17:40
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I ended up using gdisk to convert the partition. I issued:
And I was greeted with this warning:
After backing up my data, I wrote the partition table with the changes gdisk made automatically, quit (w, then q), and rebooted.
Booting into Lion was normal, but when I tried to resize my partition table with Disk Utility, I saw that I had a minor volume header error.
Well, I rebooted and used -s to boot into single user mode. From there, I issued a trusty:
Now all is well. I have a happily resized Mac OS X volume, and I can proceed with my Mountain Lion upgrade.