Public Folder Hybrid 2010 Designe

Hi@all

i´m planning a Hybrid Environment between Exchnage 2010 onPrem and Exchange Online.

But one Thing regarding Public Folder Access is at least a bit unclear.

Dokumentation say´s,

To gain Public Folder Access i have to install the CAS role on backend to realize RPC Access.

I currently have

2 Frontend Systems (HT/CAS with WNLB within an CAS array)

2 Backends (MB role DAG)

In Exchange 2010 only Mailbox Stores are able to join DAG functionality.

PF Stores are one per Server with normal replication to have fault tolerance.

My question is,

Should i install the CAS role on both Backends?

because i don`t want to let user see the two identical PF DB´s at the same time.

A fault tolerance would be great, but as far as i understand the CAS role must installed on every System that host a PF DB, to Show them to users.

But also when the PF DB`s are identical (replicates) ?

Best regards

Klaus