Multiple Unity Servers

Unanswered Question
Oct 4th, 2007

Customer has almost 15000 mailboxes they want to migrate to Unity.I have some design questions on this.We can get 15000 mailboxes with 2 or 3 Unity servers with Digital Working. I know For Digital networking all these servers should be in same AD Forest, same Exchg admin group.

Customer also wants redundancy in Exchange and Unity, we can do this with Exchange clustering and Unity failover correct??.

I have more questions on this

1. Can we have just one exchange server (exchange cluster) with one AD domain.

2. Can we install 2 or 3 Unity servers to one exchange server.In other words can we have same partner exchange server for all the unity servers in the network.

Since they want redundancy in exchange and Unity there may be too many servers and I'm just trying to reduce total number of servers they need to maintain.

3. since it is the same AD can we use the same user accounts to install/admin/service for all the Unity servers.

I want the pro's opinion and best practice to give a better solution to the customer.

Thanks in advance for everyone.


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Tommer Catlin Thu, 10/04/2007 - 11:30

you can get away with barely 2 Unity servers, but go with three to be safe.

Create an Exchange Cluster. This will give your Exchange servers high availability. Having one Exchange server, servicing 15k mailboxes is a little tough to put all your eggs in one basket. Exchange Cluster with a SAN is the way to go. MSFT has documents on how to accomplish for best practice.

If they are all in the same forest, same AD, you just need to run schema once, add service accounts for AD once.

(1) failover server per Unity server. So if you had 3 unity servers, 3 failover servers.

Come up with a scheme for your Unity servers for subscriber accounts. Geographical regions, or A-M on server one N-Z on Server two. (if that works)

good luck!

balukr Thu, 10/04/2007 - 13:30


Thanks for your response just to confirm we can have just one exchange cluster to install all (3) Unity servers but we need separate accounts for each Unity server.

FYI..this is not going to be geographically separated it is all in one campus.

Thanks Again,


Tommer Catlin Thu, 10/04/2007 - 13:39

If all the Unity servers are in the same room or campus, then (1) Exchange Cluster is fine. Just scale your Exchange Cluster and Active Directory to service 15000 accounts. Typically, if you are using Voicemail only, plan on putting in (2) Active Directory Domain Controllers. This will create backup copies of AD and also help with AD directory information requests from Exchange, etc.

Since the Unity servers in the same domain, there is no need to have multiple service accounts. Just create the accounts ONCE, then re-use these accounts for the next (2) Unity installs.

Digital Networking is optional between these three servers, but fairly easy to do since it is all one site, etc.

balukr Thu, 10/04/2007 - 13:55


Thanks.. I will talk to customer about having two DC's that brings up another question can we install AD,DC and exchange server in one box(even though MSFT doesn't recommend that)?

So I can get away with two servers for AD,DC and Exchange and 3+3 servers for Unity.

Even with this we have 8 servers already!!

You also mentioned Digital networking is optional, how Unity servers will talk to each other then or how subscriber in Unity A will talk to Unity C ?

Thanks again for your help.

Tommer Catlin Thu, 10/04/2007 - 14:04

You can put it all on box, the problem is that if that box goes out, you lose all AD information, and trying to rebuild AD and Exchange on box is going to be tough. That is why we typically recommend adding a DC just for AD replication. (and taking the load of the exchange server)

With 15K and VMO, you have to have about 8 servers. You can get away with probably (3) unity, (1) Exchange server, that is pretty risky with that many subscribers.

With digital networking, subscribers can forward and or send voice mail messages to other subscribers on all (3) unity servers. This helps with the directory. If you call the Directory Handle, it will know how to connect the caller to any subscriber from all (3) Unity servers.

Check out the Unity Guide, it's really good at describing this.

balukr Thu, 10/04/2007 - 14:19

I guess I have to go with 9 servers if they want redundancy every where with 1 AD, 2 DC with exchange (cluster) and 3+3 unity servers.

Thanks again for your help.

Tommer Catlin Thu, 10/04/2007 - 14:25

I just did a visio for 15k also for a client.

(3) Unity servers

(3) Failover servers

(2) Exchange servers clustered

(2) Domain controllers

I maxed out the ports in the design also at 144 per server just to be safe.

balukr Thu, 10/04/2007 - 14:32

Wow we need 10 servers total!!

Thank you so much for your help..

I have a clear picture now.

balukr Thu, 10/11/2007 - 08:31

I have one more question in the same scenario customer has a remote site with 300 users on a Gig link and they want a separate Unity cluster there.I was planning to add a server for DC/Exchange and Unity cluster servers at the remote site.

So now Main Site will have two DC servers and 2 servers for Exchange cluster and 3 pair of Unity servers and Remote Site will have a DC/exchange and pair of Unity servers.

Now my question is

1. If we have Exchange cluster at main site can we still add another Exchange server at remote site as part of the same exchange domain/routing group.

2. How many Unity servers we can do Digital Networking ?Is there any limitation for number of Unity servers?

Tommer Catlin Thu, 10/11/2007 - 08:47

I think there is a limit on the how many Unity servers, but it's hard to hit it.

Ideally, Unity and Exchange so be located on the same LAN. But since you have a GIG link between sites, it's basically the same thing. Just make sure you have >10ms roundtrip times or minimal latency.

Typically, the site is huge, and has certain business requirements, we will add an Exchange an DC server out at a remote site. But this is for voicemail only. Then do Sites and Services in AD to create the sites, and MTA for Exchange. If you have a GIG link with 300 people, there really is no need to have a separate Unity server out at the remote site. You have plenty of bandwidth, minimal users, etc. I would say the breaking point is 500, but that is your call.

Yes, you can still add another Exchange server to the Exchange Org. No problem. Just follow the MFST guidelines and you are set. (adding new Exchange server to the Org.

If you add the Exchange server, just remember to setup Sites and Services for Message Transfer Agent (MTA)


balukr Thu, 10/11/2007 - 08:59

As usual you were really quick on responding I really appreciate that.

Customer wants a Unity and Exchange server because these sites are 150 miles apart and Fiber has been cut couple of times in last 3 months and they don't want these users left without VM. This site has potential to grow more than 500 users by next year.

Sorry to go back again on Exchange so if we built the Exchange as Cluster at Main site we can still add a Exchange server at remote site correct?? in other words since exchg is built as Exchg Cluster will that affect anything on adding a exchg server at remote site.

One more thing does it have to be less than 10 ms for RTT?

Again thank you so much for your help.

Tommer Catlin Thu, 10/11/2007 - 09:27

So if the users are left without voicemail, does the router onsite have SRST? Because you can program the SRST router to roll the call after 4 rings back out the local PSTN, and into the datacenter where Unity resides. The voicemail will be there waiting for them then. The MWI lights may be out of sync for 24 hours or until the next sync, but big deal. Fiber was cut right?

>10ms on any LAN is ideal for connectivity.

Think the Exchange Cluster as (1) Exchange server in the Exchange Org. If you add other servers, it will it be listed in the Exchange Org.







balukr Thu, 10/11/2007 - 09:43

Since there are lot of potential for growth they have a SUB CM there at remote site.

Since Unity servers can operate with minimum features when they lost connection to partner exchange server I might give that option also to customer to go without Exchange because that should cover VM.

Thank you so much for your help.

Tommer Catlin Thu, 10/11/2007 - 09:45

Right, Unity at the site without Exchange can still take messages, hold them, but no retrieval, until the Message store (your Exchange cluster) is back online or fiber is back up. CallHandlers maybe crucial to in the design. This is another reason I put Unity at the remote site.


ranpierce Thu, 10/11/2007 - 09:51

I have to jump in on this now as I have been reading, if I understand correctly what you are saying and you might suggest to the customer UMR (not connecting to the partner server) I strongly do not suggest this.

Unity does need a message store. Many features will not work without it.


balukr Thu, 10/11/2007 - 10:01

Thanks Tom and Ran..

Yes I'm aware of that UMR limitations.I just want to give this is an option in case they don't want to add a exchange server at remote site.

I think it all depends how much redundancy they want for VM and main thing cost involved for this full project.

Thanks again.

Tommer Catlin Thu, 10/11/2007 - 10:22

Yeah, he was looking at *not* putting a local Exchange server for Unity, but have it connected back to the cluster at the datacenter or HQ. The link is a GIG fiber PTP.... so it should be fine, even though best practice says Unity/Exchange LAN.. it's basically the same have a GIG fiber between the sites.

ranpierce Thu, 10/11/2007 - 12:52

Gig fiber is fine as long as there is an Exchange message store as the partner server. But I thought that there was discussion about not connecting with the partner and thus staying in UMR mode. Maybe it was just me reading into it though.


ranpierce Thu, 10/11/2007 - 12:47

I gues what I mean then is it is not a supported configuration and if there are any issues you will not get help from TAC.

It is not worth the cost savings.


Tommer Catlin Thu, 10/11/2007 - 13:00

You can have the message store and the Unity server split if it is approved of prior by Cisco and the Account Team that reviews it. Typically TAC would not support this config, but since it is a gig line, what difference does it make if there is GIG at the LAN or GIG through the WAN? None in theory. We did Unity with Notes and split it, but before splitting the Notes and Unity server, we had Cisco sign off on the design before hand. It was a large customer and they had no problem with it after final review.

ranpierce Thu, 10/11/2007 - 13:20

I totally agree with you :-)

I just wanted to be sure that there is a partner server with a connection.

TAC won't agree to a exchangeless/dominoless message store.


dan.cavanaugh Mon, 03/03/2008 - 14:09

Do you have any references to technical documentation discussing message store limits on the exchange side of things. Cisco's docs dont really address the exchange side of things. In this specific discussion you are trying to handle 15K subscribers. Unity can handle 7500 on the front end but realistically is (1) Exchange cluster of (2) servers enough? Why not 3? Thanks.

mothiamalrajxyz Thu, 02/21/2008 - 10:02

Hi Bala,

Have you finished this design and approved from the Customer.By the way have you been working in Kenya anytime.


balukr Thu, 02/21/2008 - 10:06

No they are still working with their server team, politics, etc..

Sorry I never worked in Kenya and I always worked in US.


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