Can I partition USB HD that already has an OS?

[Riku7]

I have an external 4TB hard drive where I cloned the operating system of a computer that doesn't work, so I can get rid of the computer. I'll want to put that system into some other machine in the future, but there's no active plan at the moment. The clone takes up 600GB and then some, so there's more than 3TB free.

Now I'm facing a situation where I need hard disk space to store large files, but I'd want to keep the OS clone perfectly intact and uncluttered, so that I won't need a massive hard disk to transfer that clone to when I have a computer to put it to.

The question is, is it safe to partition a hard drive that has an OS clone on it? Or does it always mean wiping it clean, or involving the risk that something gets corrupted? Of course I wish I had done that before the cloning, but that was some time ago.

 

[chown33]

You can copy the OS clone to a disk image. Make them in Disk Utility:

Disk Utility User Guide for Mac

Learn how to use Disk Utility on your Mac to manage APFS volumes, test and repair disks, erase disks, and more.

support.apple.com

Expand the Table of Contents, and look under "Store data on disk images".

You can make the disk image on any other convenient storage device, such as USB thumb drive or an SD card.

After making the disk image, mount it (double-click it), then use your cloning software to compare the original with the clone. I think CCC can do this, but I've forgotten.

 

[Fishrrman]

You might be able to use a version of "iPartition", which is now free.

There used to be two very useful utility apps for OS X:
- iDefrag
- iPartition

Both were published by a company called Coriolis Systems that has now discontinued them, because changes in the Mac OS and the move from platter-based drives to SSDs has diminished the need for the above apps.

However, some folks may still have a need for them.
Coriolis has graciously made available all previous versions of their software.

You can freely download them from here:

Coriolis Systems