Partitioning A Hard Drive On Mac Running OS X Lion

  • Sharebar

Partitioning Mac’s internal Hard Drive running OS X Lion can sometimes be tricky. This is especially true when you are trying to partition a Hard Drive that has an encrypted partition.  Do not worry, this article has you covered in case you  run into any issues while partitioning.

Note: Before you begin this process, make sure to backup the contents of your entire Hard Drive to an external Hard Drive.

Mac’s come with a built in Disk utility tool called “Disk Utility”. This utility can be accessed using the GUI (Graphic User Interface) or CLI (Command Line). The CLI version has more options compared to the GUI version. But for our purpose, GUI version will suffice.

To partition your Drive, launch “Disk Utility” from Finder > Application > Utilities > Disk Utility. Now select your internal Hard Drive (usually the first Hard Drive in the list) and select the “Partition” tab, as shown in the picture below.

partitioning 1

Now select the number of partitions you would like to create from the drop down box. Alternatively, clicking the plus sign below the partition layout will split the selected partition into two. You can fine tune the size of the new partition by selecting it and entering the size you desire in the “Size” box to the right of the partition layout. You can also name your new partition in the “Name” box. Once done, click “Apply”. To make any corrections, click “Revert” and start over.

partitioning 2

Once you click “Apply” you will be asked to confirm your decision one last time, this is the time to abort if you are unsure. If you are sure click “Partition”. There is no going back after this. Note, if you are partitioning a brand new Hard Drive and recreating all partitions from scratch, you will be asked to select the type of partition table. In this case, select the “GUID Partition Table” radio button and click “OK”.

partitioning 3

Finally, you should see the number of partitions you created. You may be wondering why I created four partitions for myself. Well I use two partitions to dual boot different Operating Systems and I use the remaining two for data. This way I can reinstall or upgrade my Operating Systems without having to backup my data.

partitioning 4

In case the above procedure didn’t work for you, it is likely that the Hard Drive you are trying to modify has FileVault turned on (encrypting the OS partition) or has another encrypted partition on it. If that’s the case, follow the below procedure to work around the problem.

Work Around #1 – Turn Off FileVault (In Case Above Procedure Fails)

First backup your Data. Next, if the OS partition is the only encrypted partition on the Hard Drive, then turn off FileVault and try the above steps again. To do this, go to “System Preferences > Security & Privacy > FileVault” and click the “Turn Off FileVault” button and follow instructions. Once complete, you should be able to partition your Hard Drive using the initial steps mentioned above.

Work Around  #2 – Backup And Reformat Other Encrypted Partitions (In Case Above Procedures Fails)

You might also run into a problem when you don’t have FileVault turned on ( OS partition is unencrypted), but have another partition that is encrypted on the Hard Drive. In this case, backup all the data on the Hard Drive and then reformat the encrypted partitions to an unencrypted format using Disk Utility.

To do this , open Disk Utility and select the encrypted partition on the left hand pane and click the “Unlock” icon. Enter the password when promted, this should mount your encrypted Drive. Next, keeping the encrypted Drive selected, jump to the “Erase” tab. Here, make sure the partition format doesn’t include “encrypted” attribute in the drop down box and then click on the “Erase” button. Once all the encrypted partitions have been reformatted to an unencrypted format, you should be able to modify your partitions using the initial steps mentioned at the beginning of this article.

Work Around  #3 – Using Linux Live CD And Recovery HD (In Case Above Procedures Fails)

In case all the above procedures fail, then you have only one option, that is to use a Linux Live CD to destroy all you partitions and recreate them using Internet Recovery mode or a external Recovery Disk. The below mentioned steps explains how. Note: You will have to reinstall OS X Lion after you are done partitioning.

1. Make sure you have all your data backed up. Create a external bootable Recovery Disk for OS X Lion. See my previous article “Creating A External Recovery Disk For Mac OS X Lion” for details. If you have a Early 2011 or newer Mac model, you can also use the Internet Recovery mode.

2. Create yourself a bootable Ubuntu Live CD. Following link explains how,

3. Now restart your machine with Ubuntu Live CD inserted and the “Option” key pressed down. From the “Startup Manager” menu select the “Ubuntu Live CD”. When prompted select “Try Ubuntu” option. Note: “Startup Manager” sometimes shows “Ubuntu Live CD” as “Windows” on the menu. Also, it take a while for Ubuntu  to boot from a CD, so please be patient.

4. Once Ubuntu is up, launch GParted  ( see picture below) and delete every partition except the first one which says “/dev/sda1–Fat32–EFI”, then apply changes by selecting the check mark. Note: This is permanent, all you partitions with OS and data will be erased. You will need to reinstall OS X Lion using Internet Recovery mode or a external Recovery Disk.

gparted 1

gparted 2

gparted 3

5. Once you are done deleting all the partitions, restart your machine replacing the Ubuntu disk with the external Recovery Disk and “Option” key press down. Now from the “Startup Manager” menu select the external bootable Recovery Disk. Alternatively, on Early 2011 and newer Mac models, you can boot into Internet Recovery mode by keeping the “CMD + R” keys pressed down while restarting you machine. Once in Recovery mode, use Disk Utility to modify your partitions as described earlier. Once you are done creating your partitions, exit Disk Utility and re-install Mac OS X Lion from Recovery mode.

disk utility 1

Update (26th March 2013): This article has been modified to ensure accuracy and provide easier work around methods.

Please see disclaimer.


Like this article? Enter your email to subscribe and receive similar content automatically each time we publish. Plus it's free!

We hate spam and won't spam you either. Your email address is safe with us!

About Vijay

Computer junky for 20 plus years and still obsessed with it. I enjoy exploring and tweaking popular operating systems and tinkering with computer hardware. Professionally, I work as a Storage Systems Administrator. When not on my computer, I love to travel, shop, read and hang out with my family and friends.


  1. Hey you sound educated in this area, here is what I got going on: I have total annihilation Mac version easily a 10 yr old game. The only working computer I have is a brand new Mac book pro with the current operating system. Trying to install this game comes an error about classic is not compatible. From what I gather is that my operating system is to old and to create a partioned drive with tiger and it should work. So I made a 100g partioned drive and now I’m trying to figure out how to bounce between drives and how to get tiger on the partioned drive. I was hoping you could email me with the next steps. Thank you very much

    • Hi Keith, so if I get this right you are try to dual boot tiger with you current OS X (guessing Mountain Lion). You can basically do this the same way I described dual booting ML with Lion in my blog – You can switch between the two OS’s by keeping the “Options” key pressed down during start-up, this will give you an option to boot either of the two OS’s. Alternatively you can also install Tiger on a virtual machine using VMware Fusion or Parallel. This will enable you to run both OS’s simultaneously. Only draw back is you will have to pay extra for VMware Fusion or Parallel. Let me know how it goes.

  2. Ravi Chivukula says:

    Hi Vijay, thanks for the informative articles on your site. I am writing to see if you can share your expertise regarding below issues.

    I have recently purchased a Macbook pro with Mountain Lion. I have not installed any applications yet, but I do want to install Parrallels and Windows OS to run some windows-only apps. I am familiar with partitioning for n/w mounting etc on Sun Unix workstations (used btwn 1990 and 1996) and moved to NT/95/XP since 1997. I used partioning on Windows due to just paranoia. From your post, I can understand partitioning on Mac is useful to separate data from OS for future reinstall.
    1) Are there any other benefits to partitioning on Mac?
    2) Are there any downsides at all?
    3) Can I resize or merge existing partitions on Mac?
    4) What partitioning config would you recommend for using Parallels w/ Windows?

    Thank you! and really appreciate your time and guidance!
    -Ravi Chivukula

    • Hi Ravi,

      Answers to Q1 & 2> Apart from a future installs, partitions can be used to protect your critical data by keeping it on a separate partition and mounting it only when required (especially when on a public network). You might also see a slight again in performance by partitioning. I haven’t really heard of any downsides.

      Answer to Q3> Yes, you should be able to re-size your drive with the latest version of Disk Utility. HOWEVER I STRONGLY ADVICE BACKING UP YOUR DRIVE BEFORE YOU ATTEMPT TO PARTITION OR RE-SIZE YOUR DRIVE.

      Answer to Q4> Partitioning a drive to create a VM using Fusion or Parallel is optional, I recommend it only to improve a performance by reducing disk contention by the host OS and VM. It is really hard to make any recommendation without knowing the capacity of your drive. Let me know what you have and I will be able to help out.


      • Ravi Chivukula says:

        Hi Vijay,

        Thanks for your responses.

        Regarding Q4> I have a 256G HD. I don’t plan to store a lot of media. Also its a quad-core 2.3Ghz cpu. Yes, I was wondering if partitioning might help performance of Parallels/Windows applications, and therefore to install Parrallels and the WindowsVM on a separate partition. Please let me know your opinion.

        Follow up question> If I were to partition a fresh-off-the box machine (i.e. only factory install of OSX ML, and nothing else), would you still recommend backing up the OS install? I did not get a OS disk in the package.

        Thanks again for your help!

        • Good idea, I would recommend resizing the drive into two partitions. Shrink the original to 100 GB and the rest for the second partition. No, you should be fine if you have no data on it. Also you do not need a recovery disk, new Mac’s come with internet recovery built in, so in case some goes wrong or your drive fails it will reinstall the OS directly from the internet as long as you are connected.


          P.S: Please do not forget to subscribe to receive update about new posts.

  3. Nikunj N. Bhagat says:

    Hello Vijay sir,

    I have just purchased a new Mac with Mac OSX ML installed. It seems partitioning HDD is better option than working on 1 partition (which I also followed on my Windows machine). How much size of HDD space I should leave for original partition (OS, now it’s 499 GB) or how much you recommend?
    Secondly, what if I want Ubuntu OS installed on any other partition? Then, how can I dual boot OSX ML & Ubuntu?


    • Hi Nikunj, 50 GB is more than sufficient for a OS partition, provided you are storing your Data on a separate partition and not on the Home directory. As far as running Ubuntu goes, I would actually suggest running it on a virtualization layer / software like VMware Fusion or Parallel, that way you can actually run OS X and Ubuntu simultaneously.