8 Replies Latest reply: Dec 5, 2012 1:54 AM by darkhorse85
darkhorse85 Level 1 Level 1 (0 points)

I will soon be using both Lion and Snow Leopard on my newly upgraded hybrid hard drive.I know that I should need to partition the drive into three 1 for Lion 1 for SL and 1 for data/applications.



  1. The problem is how is how much space should I give each partition?
  2. Has anyone done this before or have any good ideas how to go about it?



Some extra info:

  • I am currently using a MacBook Pro (mid 2009 13")
  • I am currently using Lion OS X v10.7.4
  • The new drive is 750GB Seagate Momentus XT 7200rpm 8GB(solid-state) hybrid drive
  • The soon to be replaced drive is a stock 250GB 5400rpm HDD


Thanks all help appreciated

  • mende1 Level 10 Level 10 (91,890 points)

    First of all, I recommend you to store applications on the Mac OS X partition, so you'll have applications for OS X Lion and others for Mac OS X Snow Leopard if you want to use different programs in them.


    It depends of the amount of programs you need. Mac OS X Snow Leopard and OS X Lion takes 10 GB of hard drive, so add the programs and you'll get the space you have to give. The rest of the storage is for the data volume

  • Kappy Level 10 Level 10 (260,735 points)

    60 GBs is about the minimum to allocate for each OS.

  • darkhorse85 Level 1 Level 1 (0 points)

    Thanks . But why do you say 60GB? It seems quite a lot, surely it would be less if I am using a 3rd partition for running my data and applications?



  • darkhorse85 Level 1 Level 1 (0 points)

    One other thing I am worried about is my Mac suddenly becoming quite complicated to use with 2 or 3 partitions. I know I have to do to this in order to run certain programs.


    I do not know fully how this will affect my user experience on the machine?



  • Kappy Level 10 Level 10 (260,735 points)

    It's important that you leave a minimum amount of free space for the OS to use. You will see anywhere from 16 to 30 GBs for your OS and iLife apps. You need enough space to allow for all your third-party applications and document files. When fully set up you may have only 30 GBs of free space which is an appropriate amount to have, but not less than 20 GBs. That makes 60 GBs a reasonable minimum size.


    If you haven't put everything in concrete, I might suggest going with a 500 GB Seagate XT hybrid together with a 128 or 256 GB SSD using an OWC DataDoubler replacing the optical drive. I suggest that mainly because using the same hard drive for the OS and Data partitions will actually make file I/O slower. Having two drives and using an SSD for the startup volume will enhance file I/O operations. Only two partitions on the SSD - each 60 GBs - fit neatly in 128 GBs.

  • darkhorse85 Level 1 Level 1 (0 points)

    Thank you for your suggestio Kappy, but I have already ordered my new drive. It is a 750GB Seagate Momentus XT 7200rpm 8GB(solid-state) hybrid drive.


    • Does EVERYONE think it would  much more than likely be better to leave out the 3rd data + apps parition?


    • I believe I have log out of my computer and sign in again to change the OS I assume this would not apply to the data storage partition? I am trying to get an idea of how smoothly a paritioned dual OS Mac would run in comparisson to what I use currently?
  • mende1 Level 10 Level 10 (91,890 points)

    If you have to use the same data on both OSes, use the third volume to store your data. If not, it's better to use an external drive. You can use the data volume on both OSes without restarting

  • darkhorse85 Level 1 Level 1 (0 points)

    Some programs I would use on both OS's but some programs would not be compatible on both OS's (not Lion anyway). Does this matter when using a 3rd partition?