Unified Messaging ramble

Question: How many Unified Messaging Servers do I need? No, this is not a joke about lightbulbs.

http://www.microsoft.com/exchange/preview/unified_messaging.mspx tells you all about what UM actually does.

First lets work out about concurrent users. Your average working day is 8 hours or 480 working minutes. Time spent leaving voicemails for internal staff and picking up your own voicemail messages per day: 10 minutes. As a ratio that is 2%. Build in a 100% additional usage and say 4% ratio.

A UM Server of decent specification (dual processor, dual core, 4GB RAM running Windows Server 2003 SP1 and a set of 15,000rpm Ultra320 SCSI disks configured appropriately) should cope adequately with at least 100 concurrent connections. Doing the maths (or math if you hail from the west side of the pond), 100 concurrent connections on a ratio of 4% user usage means one UM per 2,500 employees. It is possible that this is under estimated but safe however any company with more than 1,000 employees would be well placed to implement at least 2 UM servers for redundancy / fault tolerance.

Can you put UM and other services on the same box? Well if SBS can combine Exchange, SQL and ISA on one piece of hardware, you can stick UM on a box with other services. But think logically - if that box goes down, you lose voicemail and any other service installed on it.

I am a great believer in distributed architecture. One box per service. Lose one, carry on at 95%. Eggs and baskets people, eggs and baskets.