My previous backup setup was simply to backup all of our data to an onsite file server running Ubuntu, and occasionally burn the most important subset of that data to a dvd and mail it to another location. Because the DVD could no longer fit all of the critical data, and because we weren't backing up very frequently, I thought changing to duplicity and amazon s3 would serve as a good way to get geographic redundency.
However, we have a very slow internet connection, and the initial full backup took around 30 hours, while saturating our connection (over a weekend). I've read that after a certain number of incremental backups, something will get messed up, and they won't be any good anymore, so it's reccomended that we do full backups around once a month. However, I don't think we can upload that much data with our current internet connection.
What do other users do in this situation? Is a full backup once every 6 months and nightly incrementals enough? What can we do to reduce the risk of corrupted incrementals? Is it likely only to be a single file that is irrecoverable if there is a problem with the incrementals?