the company I work for is looking into exchange 2010 deployment or office365. We have multiple datacenters however our storage is not shared across(so no windows cluster). What is the recommended way of setting up exchange between 2 datacenters for failover?

Also what licenses would it require? We only have about 25 users with maybe growth to 40 users by the end of the year.


It goes wihtout saying, that you'll need at least 2 servers (preferably 4), to achieve what you describe. This is just an (easy-to-manage) example, where each server holds HUB,CAS and MBX roles:

2 identical physical servers, one in each datacenter.

  1. Install the Hub Transport Server, Client Access Server and Mailbox Server Roles on each server.
  2. Create a CAS array to ensure Client Access to mailboxes.
  3. Create a Database Availability Group, and set up Mailbox Database replicas
  4. If you have the resources (like 2 extra servers), you might want to consider publishing OWA and other Client Access features through a proxy, preferably a Forefront TMG Server 2010 array. You might wan't to combine the Edge Transport Role and the TMG Server in one, see this link

In this scenario you would need 4 Exchange Server 2010 Standard Server licenses and 25 Std CALs. If you wish to use the Forefront for Exchange security features, I would probably go for Enterprise CAL's (they include Forefront for Exchange + Forefront Endpoint protection for all the clients). Beware that the 2 servers used for the CAS/MBX roles need to be Enterprise or Datacenter Edition servers, in order to set up the Site Resiliency features (requires Failover Clustering and NLB)

That all being said, with 25-50 users, and HA as a high priority, I'd definitely say: Go O365! Unless you have a specific need for a custom setup or any "on-premise" demands, so to say, there's not many reasons not to buy a cloud service instead of hosting it yourself. Then again, depends on your needs and your resources

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  • So in your scenario we would need to purchase 4 x exchange 2010 standard licenses and then also 25 standard user cals correct? – Chris-AZ Mar 19 '12 at 16:14
  • That should do it, but see my update – Mathias R. Jessen Mar 19 '12 at 17:28

For Exchange 2010, shared storage is no longer a requirement. Software replication was added as a feature of Exchange 2010 and is working a treat for us currently. What you are looking to setup is call a DAG (Database Availability Group). The following technet article touches on the basics of it.


I believe that the latency and throughput of your datacenter links will determine the ability to do a live failover. Otherwise you may need to consider a delayed replica in your secondary site.

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  • I have < 10ms between sites. Do I need enterprise exchange or can I get away with just standard? for only 25 users with such little growth do I really need seperate CAS,hub,mailbox servers? – Chris-AZ Mar 19 '12 at 15:40
  • @Chris-AZ The only features you get with the enterprise edition is support for more than 4 databases. You'll probably do fine with 1 or 2 databases. – pauska Mar 19 '12 at 15:44
  • With that latency you'll be able to do a live failover of the database(s) no problem. Makes rolling patching a breeze. Enterprise isn't need in your case with the small amount of users you have. – Tatas Mar 19 '12 at 15:49
  • Awesome. Is there a recommended guide/config out in the internet somewhere for less than 50 users? Usually most of the ones I find are for like 10,000 :) – Chris-AZ Mar 19 '12 at 16:02
  • Well, I haven't seen any "guides" per se. Any yes most talk is about larger installations, but I'd say it's safe to assume you can do everything on one server. I'd personally recommend keeping your actual Exchange infrastructure privately addressed and add a TMG server or something like it to be a reverse proxy for you. A service like that has a whole host of benefits to it. – Tatas Mar 19 '12 at 16:24

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