View Full Version : Create partition on external HD without erasing existing data in Lion

Sep 5, 2011, 07:45 PM
Hi there,

I just wanted to double check that I can create a partition on my external hard disk (with my back up on it and some other things) without losing all the data on it by using Disk Utility in Lion.

Thanks in advance,


Sep 5, 2011, 08:59 PM
Sure. Disk utility will let you change the size of exising partions, and add new ones in the space just freed up, without erasing your data.
It's pretty good about telling you when you've done something that can cause data loss. Take things slow, and read the Apps' messages in the partitioning pane, and you should suffer no data loss.

Sep 6, 2011, 03:34 AM
I think it depends on the type of partition table used for the external HD.

Resizing partitions on an MBR drive was never possible in Disk Utility. And I'd bet that it still isn't in 10.7. With all the things they took out of Lion, it'd be ridiculous if Apple now started to support manipulating the ancient, cumbersome and limited MBR format.

However, if you purchase an external HD, it will still almost certainly be pre-partitioned with the MBR scheme by the manufacturer, and a simple reformat of this partition will still leave the disk using the MBR scheme.

So there's quite a chance that Lion's disk utility will not be able to non-destructively create a partition on your external HD.

Sep 6, 2011, 05:46 AM
Either way, you need to have a back up - just in case. Whenever you do any disk work its a good idea.

Sep 6, 2011, 07:05 PM
Thanks for all your responses. I successfully used Disk Utility to partition my External HD and everything went as planned.

Dec 28, 2011, 09:31 PM
How did you get the nondestructive partitioning to work? I have a 500GB FAT external HD (by verbatim) and repartitioned. I did not see any way to simply resize the existing partition. In the partition tab I had to use the drop down menu to select 2 partitions (it was on "current") and this resulted (ultimately) in the existing data to be erased. I did back up so no problem, but it does not appear to me that you can nondestructively repartition a disk. Can you help?

Dec 28, 2011, 10:21 PM
I've a 1TB drive with a variety of partitions on it. When I open the partition tab in Disk Utility, all the Mac formatted partions show in the layout image with a little draggy tab thing in their lower right corners.
The ExFAT and MS-DOS (FAT32) partitions have nothing in the corner of their images that would let me resize. I think that you can only do lossless resizing of Mac native partition types with Disk Utility.