I had the genius notion that it would be simple to set up my new 2011 MacBook Air to dual-boot Lion and Ubuntu. I started creating a 20GB partition, but somehow in the process, Disk Utility crashed. The Macintosh HD volume then displayed as having 20GB less than it should. Resizing it in Disk Utility only gave errors about "free blocking space", which I assumed resulted from Disk Utility crashing during partitioning.

I said screw it, and backed up my computer on an external HD with Time Machine. I booted up my Air into the "Recovery HD" and wiped the hard drive. Now, I want to resize the "Macintosh HD" volume to its full space, so I can then reinstall Lion on it. However, every time I try to, Disk Utility says something along the lines of "couldn't unmount disk". What am I doing wrong?

Here's what I have available to solve this:

  • A 1GB flash drive
  • A non-existent CD drive on my MacBook Air

How can I fix this problem? I could do a clean install of Lion, but that wouldn't fix the issue, right?

  • I suspect the 20G goes to the recovery partition. Otherwise when in Recovery HD it should not attempt to umount it. Mayby you should try Apple's recovery hd assistant to create a recovery hd on your usb flash drive and boot from it, and see if you then be able to do anything with your main hd. – jeffgao Sep 7 '11 at 18:37
  • @jeffgao: How do I get to the Recovery HD assistant and create a Recovery HD on it? – element119 Sep 7 '11 at 18:45
  • you can get it here – jeffgao Sep 7 '11 at 19:23

I fixed it! I erased "Macintosh HD" while in the Recovery Tools, and then reinstalled Lion, and then I could resize the drive! Hooray!

  • Glad you go it working! – peelman Sep 8 '11 at 3:21

Your Recovery HD partition is on the same physical disk are your Macintosh HD partition. Depending on the operation the installer is trying to do, it might not be able to do the resize due to that (in theory that shouldn't be happening, but working off of what little information we have, that's what I'm going with).

Ideally what you should have done was to first and foremost, partition your Time Machine drive to have an 8-10GB partition you could then restore Lion's InstallESD.dmg image file to, effectively creating a bootable Lion installer disk. Then, all you have to do is plug in the external, hold option, and boot the laptop from the external drive, and you could install Lion and do your partitioning all at once. the 1GB thumb drive is almost useless, as it doesn't have the capacity to restore the disk image to.

Basically you need to try booting from an external device, and repartition the entire drive (you might as well go ahead and create your Linux partition, kudos for having splurged for a drive big enough for that to even be feasible).

You might even be able to pull off a net boot:

(and @jeffgao, the recovery partition, IIRC is a relatively small amount of space (650MB). Odds are the space is sitting unallocated, the Recovery partition wouldn't have "eaten" the 20GB.)

  • Ok, I have a 1TB external drive I can partition- since I don't have InstallESD.dmg, how do I download something onto a partition of the external drive that I can boot from to fix the current HD? Is there somewhere I can download Mac OS X Utilities, or would it be easier to stick Ubuntu on the external drive, boot that, and use that to fix the HD? – element119 Sep 7 '11 at 20:07
  • Just had a thought- would a way of doing what I stated above be partitionin my external drive, and copying the contents of the Mac's HDD (and supposedly Recovery HD), then would I be able to run Recovery from the external drive? – element119 Sep 7 '11 at 20:09
  • The bigger issue is that you don't have a copy of Lion somewhere you can get the InstallESD from. Can you still boot to OS X at all? You might have to try to do the remote restore, where the Firmware will essentially create a ramdisk to boot from, enabling low level operations like a complete repartition to take place (it sounds like when DiskUtility died it might have corrupted the partition table or at least screwed it up enough where you're seeing what you're seeing). – peelman Sep 7 '11 at 20:19
  • Ok- no, after I wiped the Air's HD, I don't have Lion at all, but it doesn't have any errors with partition tables after I "repaired" it in Disk Utility. It just won't let me resize the drive. How do I do a remote restore? – element119 Sep 7 '11 at 20:23
  • If I copied the InstallESD.dmg from another computer, would that work? – element119 Sep 8 '11 at 2:27

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