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

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Level 7

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

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.

Posted on Feb 1, 2013 3:54 AM

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Answer 1

Ian R. Brown Author

Level 7

21,066 points

Feb 1, 2013 2:08 PM in response to Ian R. Brown

BUMP!

Before this question disappears into oblivion (it was already on page 6), I would like to give it one last chance to receive an answer.

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Answer 2

Kurt Lang

Level 9

58,116 points

Feb 1, 2013 2:11 PM in response to Ian R. Brown

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.

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Answer 3

Ian R. Brown Author

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21,066 points

Feb 2, 2013 2:41 AM in response to Kurt Lang

No Kurt, my 2008 iMac shipped with . . . whatever was around in 2008. 😉

I recently upgraded from Snow Leopard to Mountain Lion doing a complete erase and clean install.

I then discovered that my scanner needed SL to achieve all its professional capability so I installed SL on a FW HD and it works perfectly on my iMac.

It's just that it might be even more convenient to have SL installed on the iMac.

If I create a partition there should be no problem installing SL if I boot from my SL powered FW HD.

My only query is whether I will be able to alter the size of the partition later, if I discover that the original size is no longer suitable.

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Answer 4

Kurt Lang

Level 9

58,116 points

Feb 2, 2013 11:55 AM in response to Ian R. Brown

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.

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.

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Answer 5

Ian R. Brown Author

Level 7

21,066 points

Feb 2, 2013 2:20 PM in response to Kurt Lang

I have created bootable partitions several times before, but I have never had cause to alter them . . . hence my ignorance.

Because I will only use SL on rare occasions, mainly for my scanner, and my iMac's hard drive is only 320GB, I was thinking of keeping the partition as small as possible . . . maybe just 10GB, but it occurred to me that circumstances may change and I might require a larger one. Hopefully I won't but it's always best to be prepared.

So just to double-check, are you saying that if I wish to resize the small SL partition I will have to delete SL and the partition's contents?

This was my concern, that either a small or a large tweak would entail complete deletion and replacement of the SL OS.

Assuming I had a TM backup of the SL partition, how long would it take to reinstate? Complete replacement of SL using an SL installer disk image would take half an hour or so.

Would replacing via TM be quicker?

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Answer 6

Kurt Lang

Level 9

58,116 points

Feb 2, 2013 2:31 PM in response to Ian R. Brown

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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