I'm trying to install Windows 7 Pro (64 bit) onto my new macbook air (OSX Yosemite 10.10.2). I'm using the Boot Camp Assistant and am at the point where it's asking me to create a partition for windows (with a slider). It won't let me reduce the Mac OSx partition smaller than 38 Gb. It currently says it's using 20 Gbs for OSx (18 Gb free), but I can't make it so that the MacOSx partition is only 20 Gb, which will give me more space for Windows.

Can someone please advise/tell me how to do this? or do I manually have to partition the drives and install Windows w/o using the bootcamp assistant.


Edit: OSX Yosemite on a Macbook Air (Early 2014). After inputting "diskutil cs list", I get "CoreStorage logical volume groups (1 found)". I just received it last week so it's pretty new. Holding Cmd-alt-r-down took about 3 minutes to boot up. I do have an external flash drive (64 gb, exfat) and I don't use time machine.

I do not plan on upgrading/using the MacOSx, I just want to have it in case I need any warranty repairs (My coworker told me you need to have OSx installed for them to run diagnostics, else they won't touch your system).


CoreStorage logical volume groups (1 found)
 +-- Logical Volume Group 0415F924-645A-47A7-B045-936E0F0AAD94
    Name:         Macintosh HD
    Status:       Online
    Size:         120473067520 B (120.5 GB)
    Free Space:   0 B (0 B)
+-< Physical Volume 536E4C17-EADB-4B7E-B71C-783BB62E2681
|   ----------------------------------------------------
|   Index:    0
|   Disk:     disk0s2
|   Status:   Online
|   Size:     120473067520 B (120.5 GB)
+-> Logical Volume Family 17DE7604-0810-4971-86F5-DDD56E0979AE
    Encryption Status:       Unlocked
    Encryption Type:         None
    Conversion Status:       NoConversion
    Conversion Direction:    -none-
    Has Encrypted Extents:   No
    Fully Secure:            No
    Passphrase Required:     No
    +-> Logical Volume 20593179-3E19-4A57-99D6-A713D13CE2FD
        Disk:                  disk1
        Status:                Online
        Size (Total):          120154296320 B (120.2 GB)
        Conversion Progress:   -none-
        Revertible:            Yes (no decryption required)
        LV Name:               Macintosh HD
        Volume Name:           Macintosh HD
        Content Hint:          Apple_HFS

Update 2: diskutil cs list now shows

 No CoreStorage logical volume groups found

but I still can't slide the bar Past 38Gb (19 Gb free) for the Mac Partition.

  • help please i'm not sure what to do here.
    – Justin
    Feb 6, 2015 at 17:59
  • I have to ask. What is the size of your internal drive? If you want only 2O Gb for OS X, then why not go all the way and eliminate OS X completely? You could just have windows installed. Feb 6, 2015 at 22:04
  • It's a macbook air so it's a 128 Gb ssd. I want to keep a Mac OSx partition because [i believe] you need to have it in case the computer needs any type of warranty support from apple.
    – Justin
    Feb 7, 2015 at 0:00
  • I posted Update number 2. Feb 12, 2015 at 0:57

1 Answer 1


Update 2:

I assume OS X is installed on partition 2 of disk 0. If you want me to check this, then post the output of the next three commands and I will verify. Otherwise proceed and attempt the resize.

diskutil list
sudo gpt -r -vvv show -l /dev/disk0
sudo fdisk /dev/disk0

To resize to a smaller size, you will have to boot using OS X Internet Recovery. (Hold altcmdR at startup.) Open the Terminal application and enter the following command.

diskutil resizeVolume /dev/disk0s2 limits

Here is an example output. Your numbers will be different.

For device disk0s2 Steelhead:
        Current size:  345.1 GB (345131147264 Bytes)
        Minimum size:  35.3 GB (35299999744 Bytes)
        Maximum size:  345.1 GB (345131147264 Bytes)

Take the minimum size and use that in the next command. (i.e. replace 35.3 with your number)

diskutil resizeVolume /dev/disk0s2 35.3G

Hopefully this will resize to the smallest possible size.

Note: When testing this procedure, I did not use OS X Internet Recovery. My 2007 iMac is just to old. I had to use a flash drive to boot the OS X Recovery System. While you can also create and use a flash drive, I just assumed OS X Internet Recovery would be easier. You CAN NOT use the OS X Recovery System stored on your internal disk. If you want to try using the OS X Recovery System from a flash drive, you will need the OS X Recovery Disk Assistant v1.0.

Update 1:

Justin if you are afraid of violating the warranty, should I assume my answers should only be Apple approved? Well, that would just lead you to following the instructions that you have been already following. So, if that is as far as the slider will go then ... that is as small as you can make the OS X partition.

On the other hand, I would remove the Core Storage and then see if you can move the slider further. Why bother with backup anything up first. You are not going to use OS X anyway. The worst that could happen is you would have to reload from the internet. Your connection speed is fairly good, so that should not take long.

Of course, it would have helped to post more than the first line produced from the distutil cs list command. I assume you either misunderstood my instructions or are really bad at using OS X. I was hoping to determine if you had a Fusion drive and/or if Core Storage is revertible. Also, I believe you need the UUID to enter the command to revert.

If you choose to keep Core Storage, I would refer you to klanomath, he is far more experianced than me. (Actually, I have no experience with Core Storage other than reading his posts.) One of us could ask him for help, or at least, his opinion.

What is the model year of your macbook air? You can find this by clicking the apple icon on the menu at the top of your screen, then selecting "About this Mac". Also, you might as well determine if you are using core storage. To do this: Open the Terminal application and type the following command.

diskutil cs list

If the output is something other than

No CoreStorage logical volume groups found

then edit your question and post the results there. Don't worry about the format, I will clean it up for you.

I assume your Mac is new enough to boot off the internet. This is where you hold the keys cmd-alt-r down at startup. What I want to know is how long does that takes? Also, do you have any way to do backups. For example, do you have a external hard disk. If so, what format and how much free space. Or, do you use Time Machine? Finally, do you have another way to access the internet, other than your macbook air? If you can not add comments to my answer, the edit your question and post the answers there.

How to proceed, depends the answers to my questions. If possible I would backup your OS X partition. Then if you are using core storage, I would remove it. Core storage is only useful if you have a Fusion Drive. Next, if internet recovery is to slow, then I would transfer my Recovery partition to a flash drive. (You probably don't even know you have a Recovery partition hidden on your internal SSD.)

If you intend to leave OS X on your internal SSD and you are able to shrink to a size smaller than 38Gb, what happens when software updates need to be installed? Or, OS X 10.10.3 comes along? If you need to grow the OS X partition in the future, then the Windows partition will have to be removed to do so.

  • @Justin, I updated my answer. Feb 10, 2015 at 21:58
  • I misinterpreted your advice. I thought u just wanted to see if the output was different than 'no corestorage logical volume groups found'. I have reedited my original question, but I will be atttempting to remove the corestorage and see if that allows me to change the slider amount
    – Justin
    Feb 10, 2015 at 23:47
  • updated, removed core storage but still can't reduce the size. thanks for the current (and future) help!
    – Justin
    Feb 11, 2015 at 0:50

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