To the best of my knowledge, there is nothing like primary or secondary server for ePO 4.5, however you can use agent handler to handle your agents for your different locations.And for backup you have to take backup of SQL DB.
Yes, there is nothing like primary and backup ePO.
If you are planning for high availability - go for ePO culstering which provides you a way in case of one server failure. If you are using virutal server for ePO - you can just schdule taking a snapshot of your server based on the recovery time (RTO) within the organization. Agent hadlers are alos a good way for high avialbility and load balancing - the disadvantage that those don't have a gui like ePO!
- Amiya Bisoi
Thanks for providing information.