You could set them up to run a Restic server for you and then do backups with that. Restic is fully encrypted, does differential backups, and can do configurable pruning. With 4 TB the initial run will take long, even locally, but it can also resume, so should work.
You could set them up to run a Restic server for you and then do backups with that. Restic is fully encrypted, does differential backups, and can do configurable pruning. With 4 TB the initial run will take long, even locally, but it can also resume, so should work.
https://github.com/restic/rest-server