Im pretty sure in 5.x you can have Exchange loaded on the Failover server now, just not on the Primary Unity server. There is a document somewhere that states this.

http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/installation/guide/vmexfo/5xcuigvmefo060.html

halfway down you can install it on the Failover server

indeed, but as i mentioned. not with UM.

this from the same doc i already posted:

Failover Requirements When the Message Store Is Installed on the Secondary Cisco Unity Server

•Cisco Unity must be configured as Voice Messaging. For information on the maximum number of subscribers supported in this configuration, refer to the Cisco Unity Supported Platforms List at http://www.cisco.com/en/US/products/sw/voicesw/ps2237/products_data_sheets_list.html.

HTH

java

if this helps, please rate

Opps! sorry I misread your UM statement in your first post.

Waseem,

Are you trying to install Unity as unified message communication or just voice mail only? There are different sets to follow.

Cheers

Ikram