DirSync and ADFS are totally different:

  • DirSync allows you to synch your AD on Office 365, that way this creates all users/groups on Office 365 based on your AD; this means 2 different accounts and password for your users, BUT the latest version of DirSync allows password sync also; there will be only 2 different accounts as soons the AD password has been synched with Office 365
  • ADFS allows you to forward Office 365 authentication request to your AD; this means YOUR AD is responsible for authentication, if your AD or ADFS become unavailable, there will be no authentication possible

You can setup DirSync WITHOUT ADFS, but you have to have DirSync for ADFS

Dirsync on Technet: http://technet.microsoft.com/en-us/library/dn441212.aspx

To download DirSync, go to http://portal.microsoftonline.com (Requires an enterprise account), then go to Office 365 Admin center, user and groups, Active Directory synchronization, setup …

Setup DirSync: https://www.cogmotive.com/blog/migration/setting-up-dirsync-between-active-directory-and-office-365