For several years now, I’ve used Mondorescue as a backup solution for those customers with a Linux server. It makes for a nice, easily scriptable backup that can go ahead and burn to disc, *(or tape or another pc….) My preferred way of doing this has been a full mondorescue backup to dvd (usually one or two discs) and a couple “incremental” backups each week. The client site handles swapping the discs as needed *(I’ve got reminder emails scripted) and they rotate through two sets of discs. Since mostly, these backups are kept onsite, once a month I burn a copy to move offsite.