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I am unable to expand my Mac's hard disk. diskutility reports this error:

MediaKit reports partition (map) too small

How can I resolve this?

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If you start the GParted live cd: On your system it will automatically detect and fix this issue. Best solution I found so far.

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Nice. I guess most recent Macs use HFS+ (Mac OS Extended), which seems to be supported for checking a partition according to its feature overview. – Arjan Feb 2 '14 at 12:59
Worked like a charm--this is the best answer--needs more up votes. – scotru Apr 28 '14 at 7:53

This blog post was the only way I found to solve it, and it's not for the faint of heart. ;-)

Basically the problem is that the GUID partition table is confused about the size of the drive. The only way to fix it is to purchase a tool that will correct the problem, or to manually correct the problem yourself by issuing commands to gpt to delete and recreate the partition table. You must create it exactly how it was before, including the partition types (UUIDs).

Also, you must be able to get a root prompt where the drive you're interested in isn't mounted. (for me, this meant popping in the install disk, booting from it, then quickly pressing Command-S to enter single-user-mode.)

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FYI, If gparted now supports this (see above answer), I'd do it that way! – Mike Sep 11 '14 at 18:10
Thank you! This was causing a nightmare for me. This solution worked out perfectly. – Tony Beninate May 21 at 11:21

I know it is a late response. Now only I faced this issue and I find out this blog INCREASE DISK AND PARTITION SIZE IN OS X. This solved me my issue. I am posting this because this might help someone else I hope.

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Why not just boot into single user mode? Hold down command+s on boot. Performcheck disk and then mount the drive.

Go to /Library/Caches and /System/Library/Caches and remove everything in those folders.

Then go to /private/var/db and remove, BootCache.playlist and .volinfodatabase. Reboot and use Disk Utility again. Just did this here and it worked moving from a 120GB SSD to a 250GB SSD. Was getting the dreaded medikit error too small or whatever.

You might just have to remove the .volinfodatabase. Try that first. If that doesn't work try the .volinfodatabase again and the BootCache files. If that doesn't work try what I tried.

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This worked by removing both .../Library/Caches, and the + BootCache.playlist – bigkm Apr 7 '15 at 5:41

New in Mavericks apparently, you can boot from the installer media (cd or thumb drive) and use it's disk utility.


  1. insert installer media
  2. Restart, keeping the option key held down until it asks you what media to boot from
  3. Select the installer media to boot from
  4. You will be presented with some options, the last of which is disk utility
  5. Open disk utility
  6. Partition as normal
  7. Restart normally

This works because it skips all the cached information about the drive that Jens Erat mentioned in his comment. You might notice that around step 5/6 disk utility will take some time to analyze your disk, which it doesn't do when you've booted normally. That's a good thing.

By the way, this does not work in recovery mode. Recovery Mode looks very similar to the booting from the install media. But recovery mode still boots off of the harddrive you're trying to repartition, and that causes problems.

(Thanks to Dennis at my job for helping me figure this out)

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