Partition a Drive Without Loosing Data using Disk Utility - Mac

Ok, so I have a 1TB drive with info on it and I decided to also set it up as my Time Machine backup drive. A few months later I realized that Time Machine will continue storing its incremental backups until the drive is filled. Well, I don't need a backup history that is so extensive. Ultimately, I needed to partition my 1TB drive without deleting the 300GB of existing information (that wasn't my TM backups).

I set up a test using another external drive so I wasn't experimenting on the data I want to preserve. Using Disk Utility I partitioned the drive preserving the sample data and even repartitioned it successfully.

A week later when I had time to partition my "real" drive Disk Utility told me that all of the data on the drive will be erased. So, I hooked up my test drive and was unable to replicate the previous partitioning that preserved the data. After reading online most sites recommend using a 3rd party application to achieve what I did with Disk Utility AND even said you can't do partition a drive preserving the info using Disk Utility. Apple's site was no help either.

I finally figured out how I managed to do this, here are the steps:

Launch Disk Utility and select the drive you want to partition. Then "shrink" the size of the drive by grabbing the lower right hand corner of the image that represents the drive and make it smaller. Click on Apply.

Next, click on plus at the bottom left of the graphic representation of your disk space and a 2nd partition will be added using up the remaining space. Click Apply.

Now you have 2 partitions and you have not lost any existing information!

I hope this is useful, I know it saved me a bunch of time!

Oh, the reason I was having difficulty repeating this is because I was going to Volume Scheme and selecting 2 partitions, which requires the existing data to be erased. The above description is a long way to create 2 partitions but it allows you to keep existing data!