How to resize a live partition in Snow Leopard and Lion

Wil Limoges takes you through the steps that will allow you to create and resize live partitions in Mac Snow Leopard and Lion.

This week I’m going to share one of my favorite tips. Using Apple’s Disk Utility I’ll show you how to create and resize a partition on a drive that contains data. Furthermore, we are going to do it from within the operating system that we are booted from.

If you're new to partitioning, live partitioning is a relatively new feature that allows you to partition a drive from within the operating system without the need to reboot your Mac from a start-up disk. Back in the olden days, you would have been required to boot from an installation disk or purchase a third-party solution to complete the task of partitioning. Since the advent of Bootcamp, Apple has added the ability to partition drives without the need to reboot into the installer.

Before we start, I feel I should provide the obligatory warning that before proceeding you should make certain that you have a reliable backup of data on the Mac that you are going to partition. Partitioning a drive on the fly like this is one of those impressive pieces of magic that Apple has added as a feature but has the potential to be very destructive.

With that out of the way, start by opening up the Finder, navigate to Applications | Utilities and open Disk Utility by double clicking it. Once open, select your drive (not the partitions located below) as I have in Figure A.

Figure A

Disk Utility

After selecting your drive, five tabs will appear to the right of where the drives are displayed.

Select the Partition tab.

Figure B

Click the Partition tab

Next, click the plus button located just below the Volume Scheme.

Figure C

Click the + button to create a new partition

This will divide your drive up into two parts. If you wish to have more than two partitions, you can continue to click the plus button until you have the desired amount of partitions.

You can then resize the partitions by moving the slider between partitions up or down, or select the partition and type the size that you want into the size field to the right of the Volume Scheme.

Figure D

The blue area within the Volume Scheme displays the data on your drive

If at this point you decide that you would like fewer partitions you can select the partitions that you don’t want and click the minus button, or if you click Revert, your partition will revert back to it’s initial state. You can also select the Format of your choosing at this point as well. Generally speaking, if you are creating a partition for Windows, I suggest that you use the Bootcamp utility instead. Otherwise select the format of the drive from the drop-down menu. I suggest sticking with the default selection unless you have a unique need.

Click Apply and Disk Utility will begin creating the new partitions.