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iPartition and Core Storage

If your machine

The chances are that your disk is in fact using something called Core Storage behind the scenes.

iPartition does not support Core Storage.

Why? Because it’s entirely undocumented. In fact, if you use the Core Storage tools in the diskutil command yourself, you can easily end up in a situation where Disk Utility will simply refuse to run, and apparently Apple doesn’t regard that as a bug.

Now, if you’re in the first situation (Fusion Drive), iPartition is not going to be terribly useful for your built-in disk. You could safely use it to resize a pre-existing Boot Camp partition, but you can’t change the size of the Core Storage partitions without destroying data.

If you have File Vault 2 enabled, you will need to turn it off before repartitioning. This should change your partition back into a normal one, but if it is still Core Storage afterwards you may need to carry on.

Finally, if you are using Yosemite or El Capitan, you may find that your boot disk has been set up using Core Storage rather than plain HFS+. Again, you can’t change the size of Core Storage partitions without destroying data, but you can convert these partitions back to plain HFS+. To do this, enter

diskutil cs list

in Terminal. You’ll get some output with a line like

        +-> Logical Volume 273CF63F-1C56-4C4C-8D7B-7C9220B7E474

and you can then enter e.g.

diskutil cs revert 273CF63F-1C56-4C4C-8D7B-7C9220B7E474

to convert to plain HFS+.

Once you have done this, you can safely resize with iPartition.

Note also that on machines that are using Core Storage, you may see your disk appear twice in the left hand pane in iPartition’s window. What is happening here is that one of the icons represents the physical disk, which is where the Core Storage partitions are actually stored. The other icon is the virtual disk that is presented to the operating system by the Core Storage layer.


Posted by alastair at 2015-Oct-13 14:10:23 UTC. Last updated 2015-Oct-13 14:10:11 UTC.