MacOS – Time capsule backups previous versions of AppStore apps

I have thought about that same problem for quite some time now. With online backups, large amounts of files are slow to upload and inconvenient to download; so I really like the two physical USB drives approach. Having both disks onsite while you clone the most recent disk is not as bad as long as you limit the time you use for this. Don't do it over a week, for instance. Get it cloned and offsite ASAP.

Having said all of that, my answer to your question is to use something like a Drobo. I haven't done it yet, but Drobo seems like it fits the bill: The Mac will see it as one big Time Machine volume, but in reality you are mirroring multiple disks at the same time. If price is not an issue, and you don't mind handling SATA drives around (You can get an enclosure for the one that will be traveling offsite) it may be something to look into.

Hope this helps.

Time Machine is using differential backups. That means your first backup is a complete backup which is same size with your drive. Starting from the second one backup will include changed files since last backup.

These Backups are accessible by finder. So you can easily find out which folders causes these big backups. After you find the folders you can manually exclude these folders from Time Machine Backup Options.

Some softwares may cause huge backups if they changes files last updated status like Dropbox Agent or similar. You may consider exclude folders of these softwares because they are already copied to the cloud.