Resizing 2 existing partitions

I have an external USB 3 1 TB drive w/ 2 partitions, both 500 GB. One partition is a bootable clone of my hard drive and the other is a backup parition for Time Machine. I'd like to make the first partition, the bootable clone smaller, and the second partition for Time Machine larger.

The rationale is Time Machine backups get larger than the source drive's data, and the clone partitions are always the exact size of the source drive.

The source drive is 750 GB, but right now is using 260 GB of space. Of course it will get larger over time. So my clone partition should be larger.

The problem is, I don't want to delete any data on the existing partitions, especially the Time Machine one. If I resize the partitions with Disk Utility, will I lose any of the existing data? Or should I backup each partition first?

I also use cloning software in addition to making Time Machine backups, however, I use two separate hard drives. And I usually recommend users to do the same.

You can certainly resize the partitions if you choose, (yes, make a backup first) but in my opinion, you would be better off and have more secure backups by keeping them on separate hard drives. Consider this: If your external hard drive fails, you've lost both your ability to boot from the clone and to restore from Time Machine. Not good.

I managed to resize the two partitions. One was easy and the other a royal pain.

The drive had 2 partitions at 500 GB each. The bootable clone partition, I changed to 350 GB. Since it was at the first partition, Disk Utility resized it easily.

The second partition, with Time Machine backups, was more problematic. I changed it to 650 GB, but the the starting point was at the mid point on the drive. So I made a sparse image clone on another drive. Then I deleted the partition and created it again at 650 GB. Then I cloned it back from the sparse image. There has to be an easier way. It took about 3 hours, even with 2 USB 3 drives with real USB 3 ports. That was with about 260 GB Time Machine data.

I agree with you about using separate drives one with the bootable clone and the other with Time Machine. But not just in case one drive fails. I want to avoid the above scenario. As my main system drive fills up, the 350 GB / 650GB partition sizes might need tweaking again.

And with Time Machine, I've discovered it really needs extra space, even though TM may release the space once a backup is complete. It seems to need scratch pad space.