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Can the size of an extra (dual-boot) partition be subsequently altered?

158 Views 6 Replies Latest reply: Feb 2, 2013 2:31 PM by Kurt Lang RSS
Ian R. Brown Level 6 Level 6 (17,420 points)
Currently Being Moderated
Feb 1, 2013 3:54 AM

I intend to add a small partition to my ML iMac so that I can install Snow Leopard in a dual boot configuration. (I realise ML will not recognise the SL Install DVD but intend to boot from an external FW bootable hard drive in order to install).


Assuming my theory works and I can install ML on the newly created partition, will I be able to enlarge it subsequently, should it prove to be too small?


Conversely, would I be able to shrink it if required?


Or will I be stuck with its original size? (I believe a "normal" partition can be resized but this one will be containing a bootable OS).

iMac, OS X Mountain Lion (10.8.2), Little knowledge... many opinions.
  • Kurt Lang Level 7 Level 7 (31,465 points)

    If I understand correctly, you want to install Snow Leopard on an iMac that shipped with Mountain Lion? If so, it can't be done. Even if you were to use Disk Utility or some other app to install a disk image of SL onto another partition, your Mac will not start up to it.

  • Kurt Lang Level 7 Level 7 (31,465 points)

    Ah! In Snow Leopard and later, it's actually really easy to create a partition, and even resize one after the fact. Here's an example. Select the physical drive (far left indent) in the left column and choose the Partition tab.


    Screen shot 2013-02-02 at 1.48.13 PM.png


    In this case, I already have two partitions. You can kind of see I clicked on the upper partition, which made a gray box around it to show it's been chosen. I can then grab the sizing corner at the lower right and slide it up to create an empty space on the drive. Since you'd be doing this to a drive with all one partition, you'll be creating your blank area at the bottom. Once you have that open space, click the + button. A new partition (by default, OS X Extended) will fill that space. If you didn't make quite as large a space as you would have liked the first time, click the Revert button and do it over. Once you're satisfied, click Apply.


    You now have a blank partition to install Snow Leopard onto. If you later need more space, you must first have a full backup of the SL partition you can restore. Go back into Disk Utility and remove the SL partition using the - button. Then do the procedure above to make a new, larger partition and restore the SL backup.


    As always, have full backup of your current drive before starting any of this.

  • Kurt Lang Level 7 Level 7 (31,465 points)

    are you saying that if I wish to resize the small SL partition I will have to delete SL and the partition's contents?

    As far as I can see, yes. You can pull a partition up to make space below it, but you can't move the top of the partition below it up to fill the space you made. So you'd have to remove the smaller partition at the bottom, resize the one above to make more room, then fill the larger blank space with a new partition.

    Assuming I had a TM backup of the SL partition, how long would it take to reinstate?

    Would replacing via TM be quicker?

    That one I can't answer as I don't use TM. I make my system backups with SuperDuper!. Then all I have to do is a straight restore, not a reinstall from the SL disk, which then has to correlate with the TM backup to figure out what needs to be pulled from there to finish the restore.


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