SFTP, rsync and Borg
Besides Proxmox Backup Server, every datastore also accepts tools that work over SSH: SFTP, rsync and Borg. They all log in with an SSH key that you add to the datastore once.
Add your SSH key
Open your datastore, click Connect and select rsync / borg / sftp:
Paste your public SSH key and click Save. The dialog also shows the user (customer<ID>) and the host that your tools connect to. Test the login before you set up a tool:
ssh -v customer<ID>@<host> -i /path/to/private-key
Use your tool
The examples use customer<ID> and <host> as placeholders. Replace them with the values from the Connect dialog.
Borg stores deduplicated, encrypted backups in a repository on your datastore. Create the repository once, then create an archive for each backup:
# Create the repository
borg init --encryption=repokey customer<ID>@<host>:./borg
# Create a backup
borg create customer<ID>@<host>:./borg::{now} /path/to/files
List your archives with borg list, and free space after you deleted archives with borg compact:
borg list customer<ID>@<host>:./borg
borg compact customer<ID>@<host>:./borg
rsync copies files and folders, and on later runs only what changed. Pass your private key with -e:
rsync -avz -e "ssh -i /path/to/private-key" /home/user/documents/ customer<ID>@<host>:/backups/documents/
-a keeps permissions, owners and timestamps, -v shows what is copied, and -z compresses the data during the transfer. rsync makes a copy, not a versioned backup: a file that you delete or damage locally is gone on the datastore after the next run too, unless you use --backup or a tool like Borg.
Any SFTP client can upload and download files. Use your user, the host and your private key:
sftp -i /path/to/private-key customer<ID>@<host>
Graphical clients such as FileZilla or WinSCP work the same way: choose SFTP as the protocol and load your private key in the connection settings.