[Duplicity-talk] Differential/incremental backups

[Rik v. A]

Hi, I've been using Duplicity for a few months now, to create weekly
backups from a backup NAS to an offsite backupserver. Machines in my
network push their backups daily and weekly to a local NAS machine.

Since storage space on an offsite server is expensive, storage
capacity is obviously limited. That's why backups snapshots are
created on the local NAS machine (using rsnapshot), because there's
plenty of diskspace on that machine. That way, as long as my apartment
doesn't burn down, I can always quickly recover a backup from a few
days or weeks ago.

This NAS copies the latest (daily) backup to the offsite backupserver,
every weekend, using Duplicity. However, since Duplicity create
incremental backups, I end up with multiple "snapshots" on the offsite
server, as well. Which uses unnecessary disk space (I already have
snapshots locally).

I could solve this by creating a full backup regularly, however this
defies the whole use of Duplicity; because our upload speed is very
limited, and traffic is expensive, we are forced to use
incremental/differential backups.

What I _really_ want, is a full backup created once, and every time I
run duplicity, it should update this backup, by only updating changed
files.

Kinda like "rsync --verbose --backup --archive --compress --force
--ignore-errors --delete" (which is the line I use to create
incremental backups from one server to the backup NAS), but with the
encryption.

According to Wikipedia
(http://en.wikipedia.org/wiki/Incremental_backup), this is not
incremental nor differential, so I wouldn't know what to call it.

So after this long story, my question is: Is this possible with
Duplicity, and if yes, how?

Kind regards,
Rik v. A