I'm trying to partition my Macbook Air's SSD for dual-boot with Boot Camp (which I've done several times before)... however, it's not seeing 10GB free, yet I have 20.56GB free as per Finder, and Disk Utility sees 10.9GB unused space.

What's going on? How can I force this to work? Can I use disk utility and image to an external drive and restore? Would vastly prefer an easier method of course


You may be just reading the wrong figure in Disk Utility, have a look at the quote below from the apple discussion forums

Disk Utility will show two different "free" readings, depending on where you look.

Sounds odd, but they're for different purposes. The larger figure, which the Finder and other things will use, is the total free space available.

The second is the amount of free space available for a new partition. It's shown when you select the top line for the drive, click the Partition tab, then select a partition, the "Available" amount may be smaller.

This is because partitions, unlike folders, must occupy contiguous space on a disk. The data on your OSX partition is scattered over it, not all nicely packed together. That's normal, as you add, update, and delete files, not every nook and cranny is used again immediately.

But whether there's 7 GB free or 18, that probably isn't enough to be adding a partition; it's probably too little for OSX to operate well. There's no "hard and fast" rule, but you should always have at least 10 GB or 10% of your OSX drive free; many folks say 15% or more.

You could back up your drive (on two different HDs, to be safe), reformat it to 2 parttions, then restore the backup. But it's going to be very tight, and you'll likely have performance problems because of it.

Try to delete anything you don't need, and/or offload stuff you don't use often and delete it.

  • Yes certainly have, and Finder sees all that space – Nektarios Apr 10 '11 at 20:59

Boot camp wants 10GB of continous space, if there is even a little file somewhere cutting that 10gb it shows the error message.

How I got around this issue:

  1. Open up disk utility and shrink your primary partition down by about 12 GB, in effect making 12 GBs of un-partitioned space. (WARNING: this might kill some data at the end of the disk but for me everything seemed to be ok)

  2. Then I repartitioned the primary partition back to the full amount, in effect creating 12GB of contiguous empty space.

  3. Run Boot Camp Assistant and no more "10 GB" error message!

Alternatively I though about looking in to defragging the hard drive.

  • Hi Todd thanks for the idea. I did try this, and sometimes it works, but sometimes it doesn't. It definitely doesn't harm any data. The way it doesn't work though is that it will try to shrink for a while, then just give up and say unable to do so. – Nektarios Apr 28 '11 at 0:06

Do you have TRIM enabled ??

If not you can do it like this: http://osxdaily.com/2011/03/27/enable-trim-ssd-mac-os-x-10-6-7/

  • Nope and that is an extremely bad idea IMO – Nektarios Apr 10 '11 at 19:02
  • Why is it a bad idea to use the TRIM function ?? – Rene Larsen Apr 10 '11 at 19:24
  • Because it's not officially supported by the OS and could easily ruin your SSD or decrease performance significantly – Nektarios Apr 10 '11 at 21:00
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    It is officially supported by the OS on the new Macbook Pro's starting with OS X 10.6.6 - and it is this TRIM support you enable with the tool. The performance and empty space re-allocation can only be better when using TRIM - but it of course up to you what you want. – Rene Larsen Apr 10 '11 at 21:40
  • I don't understand how TRIM will solve this problem, though. – asmeurer Oct 28 '12 at 7:16

See solution at http://datafilos.blogspot.cz/2012/04/boot-camp-assistant-error.html that helped me.

  • 3
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10.9 is perilously close to the 10GB required. I suggest you arrange things so you have 12GB reported free by Disk Utility and then try again. However, I'd be more concerned abot the reporting discrepancy.

The fact you have Finder reporting a different amount of free space than Disk Utility tells me something is screwed up with your data. They should both report the same. I would think it worthwhile to backup your disk, reformat it and copy your data back, file by file. Better safe than sorry.

  • I did a check of the FS and there are no issues, I've had similar things happen in the past. I got disk util to see 14GB free now but Boot Camp Assistant still doesn't have 10GB available. It's issues with how partitioning seems to work in OSX I guess where you need contiguous free space at the end of a disk – Nektarios Apr 11 '11 at 0:05
  • I don't think you can assume there are no problems with your data, Finder and Disk Utility should report the same freespace, The fact they are not indicates to me there are files that you have deleted but are still showing up somehow. I think you need to backup, reformat and reinstall. That should solve your problem. – Stefan Youngs Apr 11 '11 at 5:40

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