Are you doing file level or image-based backup?

I'm not sure, how can I tell?

By plan name, plan icon, or configuration info

Thanks that worked!
Now, it seems that the amount of space taken by the backup is MUCH larger than the actual size of the files backed up. In the screenshot you can see that the aggregate file size is 14.9 GB, yet the size on disk is a whopping 28.5 GB! Any idea why?

It's hard to say, as I'm not sure what is your backup type and configuration. 1. Are you running Image-based or file-level backup?
2. Are you using New Backup Format or Legacy?
3. What are your schedule and retention settings in the plan?

Without this information, I can't answer.

Sure:
1. I believe it's file level backup because I see a folder icon next to the name of the backup.
2. I'm using Cloudberry Backup Desktop Edition which I believe is no longer supported, so I guess it's the legacy version?
3. As to the settings, I have it on manual backup to a local external drive, custom mode, fast NTFS scan, back up all files in selected folders (but not system and hidden files or on-demand files), after 90 days delete files that have been deleted locally.

Thanks for providing this information. So if you want to stay on the file-level backup, you can use simple mode. It will just copy what you have on your disk. The simple mode doesn't allow versioning, retention, encryption, compression, etc., but it will back up the latest version of your files, and the backup size should be very close to the size of your source files.

You can switch to image-based backup if you want a system snapshot for full system recovery.

Yes, in this case that's all I need. But I AM using simple mode, and while my data occupies 200 GB, the data on the disk occupies over 300 GB. Crazy.

custom mode, — Robin Gray

Are you sure you are in simple mode?

after 90 days, delete files that have been deleted locally. — Robin Gray

Have you deleted any files locally during the last 90 days? They might still be in the backup storage

No, sorry, I am in custom mode. I can re-do the backup in simple mode, but as I remember it was the same. I thought custom mode was simpler than simple mode?
(The backup was only done a couple days ago, so I don't think file deletion would have much effect on it, especially given that no large files have been deleted since the backup was created.)

I now did the backup in simple mode, and the result is the same: i.e. the space on disk is considerably larger than the file sizes, by around 50%-100%.