I need to better understand the backup process under SQL Server 2008. Since drive space is a kind of matter for us and we want to have a better disaster recovery solution, I decided that we will implement differential backups throughout the day (every hour).

Am I right to think that if I keep the recovery model of my databases to Simple, the differential backup will be almost the same size as Full Backup (too big to make one every hour) ? I already tried to switch to Full recovery and it seemed to have fixed the issue (differential backups were way smaller). I heard that the recovery model must be set to Full to use Log backups (to the minute recovery etc., but we don't need that) but never about differential backups.

So, is the recovery model really having an impact on differential backups or am I missing something ?

Thank you