Owncloud is NOT a backup solution, it is a remote access/sharing solution. At least one client syncing to an account on the Owncloud server should have an incremental backup solution. My personal setup is that my OSX clients backup to a Time Machine. Easy peasy. If I have a server-side failure, I keep motoring on, albeit without remote access/sharing until I get the server fixed. If I have a client-side failure, I can restore to a prior moment in time off the Time Machine or sync to a new client off of Owncloud depending on the nature of the failure.