How can I safely create a partition to an already bootable drive

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How can I safely create a partition to an already bootable drive

Hello everyone,

I recently bought an external drive of 500Gb with the intent to use it to store large files that I use on my Mac and to use it as a bootable drive for Windows.

I followed this tutorial to make the drive bootable on Windows 10, everything works well for that part.

Now I want to be able to partition the drive so that I can have 2 parts for Windows (1 part that contains the infos for the boot, 1 that contains Windows) and 1 part that I can use on the Mac side to store files. I thought that I could simple use the partition operation on the Disk Utility app, but the operation is greyed out. I found many answers on forums, but none of them is exactly what I'm looking for. Any idea how I can can achieve it ?

The actual state of the drive :

Thanks in advance and have a good day !

MacBook Pro (Retina, 13-inch,Early 2015), OS X El Capitan (10.11.3)

Posted on Jun 13, 2016 5:52 AM

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Answer 1

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Loner T

Level 9

59,513 points

Jun 14, 2016 11:00 PM in response to Tørrak

This disk is an MBR disk with a full NTFS partition using the entire disk. Disk Utility cannot resize a NTFS partition.

You will need to either create a partition after Windows is installed, or erase the disk, and convert it to a GPT disk, partition it first with one part for Mac, and then run the steps in the tutorial on the part for Windows.

If you look at step 12, it is using the remainder of the disk completely.

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