How do I resize an APFS Container

You can't without repartitioning the drive. Containers are hard breaks in the space mapping. Such as here:

It's impossible for me to move the dot to the right of Catalina because (at least in part), there's live data sitting right next to it, as indicated by the gray lines. It's also a hard break (standard partition) that can't be changed to a larger size without repartitioning.

Not sure why it would be a bad idea to use containers on an external drive. A drive is a drive is a drive. I have my external SSD broken into four containers. I have both Catalina and Mojave on the drive. Plus I keep other data separate from the OS partitions. I don't see how it makes a difference if you use containers or partition groups. Other than they're not sharing the same free space.

iwaddo wrote:

used for exclusively for Carbon Copy Cloner.

I chose APFS for this drive so that I can use the Snapshot facility offered by Carbon Copy Cloner...

suggested by Bombich.

... I just want to enlarge the smaller container. I want to use the 20Gb used by Container disk8 (which I created by making Container disk7 smaller) and add it to Container disk6.

My best advise is to contact CCC for their excellent customer service & support:

"The most effective way for us to help you resolve a problem is if you submit your request from within Carbon Copy Cloner. Open CCC, then choose "Ask a question" from CCC's Help menu."

ref: https://bombich.com/kb/ccc5

Please post back with your final success or failure— it could well prove to be most informative for all here.

Good luck !

My take on a robust backup plan is you are better off with multiple smaller drives compared to one single large drive—all drives will fail in due time—some new out of the box.

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

Boot clone https://discussions.apple.com/docs/DOC-10081

How to use Time Machine to back up or restore your Mac: https://support.apple.com/en-us/HT201250

Use DiskUtility Restore feature  https://support.apple.com/guide/disk-utility/restore-a-disk-dskutl14062/mac

note:  >System Preferences>Security & Privacy >Privacy>Full Disk Access

unlock the  padlock,  press the + button and add Disk Utility 

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iwaddo wrote:

This gives me a good level of confidence, not sure what else I could do, though I do have a spare 4Tb drive so I am thinking of either doubling up my Time Machine or Carbon Copy Clone.

Thank you for your help

Good computing iwaddo.

Thanks for using the Apple Support Communities in an effort to resolve your issue.

iwaddo wrote:

I have an 8,000Gb external drive. It was originally split into two containers, of 30Gb and 7,970Gb.

The 30Gb Container is bootable, therefore, it has a boot and data Volume.

The 7,970Gb Container is just data.

I want to remove 20Gb from the large Container and add it to the small Container.

Using Disk Utility I have reduced the large Container by 20Gb to 7,950Gb, this created a third Container with a single Volume of 20Gb.

What I am unable to do is make the 30Gb Container larger, Disk Utility just ignores my request to make the Container any larger, presumably because there is nowhere for it to grow.

If I indicate to Disk Utility that I want to delete the 20Gb Container it assumes I want to add it back to the larger Container and does not seem to allow me add it to the smaller 30Gb Container.

Does this make any sense? Any guidance appreciated.

Hmmm... and what is this drive used for(?) and how is this drive formatted.

Containers and apfs is not recommended for external drives... Documentation from Apple on apfs is scant to none as you may well know.

 Apples new concept & the APFS container. All APFS volumes reside within a container, and the container resides within the disk's partitioning scheme. All volumes within a container share the space that is available to the container; separate APFS containers do not share space with each other.

If you want to press on, you can read more: Working with APFS Volume Groups

please advise...

The recommended file format continues to be the old reliable HFS+ file format [for mac only patition type GPT (GUID).]

Types of disks you can use with Time Machine on Mac - Apple ...

About the read-only system volume in macOS Catalina - https://support.apple.com/en-us/HT210650

Use external storage devices with Mac - Apple Support

File system formats available in Disk Utility on Mac - Apple ..

Partition a physical disk in Disk Utility on Mac - Apple Support

Backup disks you can use with Time Machine - Apple Support

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

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