Looking for backup device advice

I appreciate your advice as you've given me something to think about. Seems like the choices come down to convenience (one big volume makes the backup easier) or higher reliability (multiple volumes to backup to which minimizes loss if one fails but makes backup more difficult). Given I intend to backup once a month and take the backup nv+ to my office when not backing up I think this should provide reasonable reliability using one big volume as I'd be able to tell if a drive has failed in the backup nv+. If that happens I'll just replace the drive and do another full backup.