Exchange Server 2013 High Availability configuration

  I want to setup Exchange Server 2013 in a high availability configuration.  My mind is spinning a bit from all the research and I am unsure of the actual process.  Most walk through docs seem to be for large corporations.  This is what I need, maybe I am going about this wrong.  I would appreciate any guidance in the planning of this environment.


Small office of 15 users.  Work with large files and rely heavily on email.  Setting up a VM host server in building 1 with a host OS of Server 2012.  The chassis will be configured for 4 VM's (unless we need something different).  

Server1 - Server 2012 Active Directory Domain Controller with normal other duties, DNS, DHCP, etc...
Server2 - Server 2012 File server with DFS
Server3 - Server 2012 with Exchange 2013
VM4 - Unused in case needed

A second identical chassis will be placed in a second building on site with a fiber link between them.  

Server1 - Server 2012 Active Directory secondary domain controller
Server2 - Server 2012 File server with DFS
Server3 - Server 2012 with Exchange 2012 (secondary server)
VM4 - Unused in case needed


The idea behind this is that we have a DC in both locations, we will configure DHCP in each location with a /24 but assign the first half of the scope from DC1 and the second half from DC2.  If we have a DC fail we should be able to keep running.

Having two files servers part of the DFS group in case on fails we are still up and running.

Resources on the chassis for future expansion of VM.

I want to have Exchange running and optimally if it goes down it fails over to another machine.  I get conflicting docs on how to set it up.  Terms like high availability, clusters, failovers.... really not sure.  Some say we need a minimum of 4 servers to have an exchange cluster.  We just want a simple backup mail server that can be up and running as quickly as possible in event of a failure.

Thanks for any advice.
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Seth SimmonsSr. Systems AdministratorCommented:
not sure if this is one you looked at already but goes into HA requirements for exchange 2013

starting with windows 2012, you can now cluster dhcp if this helps any
David CarrCommented:
In Exchange Server 2013, high availabilty is achieved by using Database Availability Groups (DAGs) to replicate the mailbox data between servers and performs automated recovery.  DAGs use Windows Server Failover Clustering Services for recovery and log shipping for replication.

The number of servers depends on how many copies you need for your environment. Seems like you need just two more copies of the data using three servers with three DAGs: One Primary and two copies.   You will also need a file Share witness per DAG which is usually on   a Client Access Server.
Simon Butler (Sembee)ConsultantCommented:
You have everything that you need for the core Exchange high availability.
The FSW can sit on the local file server. No need for another server.

When it comes to the Exchange configuration, just install the pre-requisites as per the Technet documentation for Exchange, then configure the DAG within Exchange, again following the Technet guides. No need to configure the clusters manually.

Four servers for a cluster? Not sure where you have read that as it is wrong.
You could use three servers, two active and one passive. However for this number of users total overkill. You would need a fourth server that you could use as an FSW if required (because of the failure of a DAG member). However that can be a regular file server, it doesn't have to be Exchange.
The only reason that using a standalone CAS role holder is because it already has the permissions, but for this number of users I wouldn't be able to justify the additional cost.

The only other comment I would make is on licencing.
Windows 2012 allows two VMs per physical host/licence. There is no Enterprise edition.
Windows 2008 R2 allows four VMs per physical host/licence on Enterprise edition.

Therefore to do what you want (with four VMs) you will need either two Windows 2012 licences per physical host, or an Windows 2008 R2 enterprise edition licence.
I "think" you can downgrade a Windows 2012 standard to Windows 2008 R2 Enterprise. Check with your software vendor.

compcreateAuthor Commented:
Ok thanks everyone for the quick replies.  I am still not 100%.  Maybe if I slim things down in what I am looking for.  All I want is Exchange to be redundant.  What is the minimum servers I can get away with to accomplish this and what config?

1 active, 1 backup

1 active, 1 cas, 1 dag etc...

When I read about DAG in technet it just says "configure a DAG server".  So I don't know if it has to be stand alone, if I have 1 main active server if I can turn that stuff on as another role and then make a second server part of the dag and thats is all I need is two servers?  

I want the simplest way to ensure Exchange is always running.

I am wondering if it might just be easier to have the second machine "waiting" and just load the VM image if the first host dies.  Just manually move it over, reconfigure it with same IP and all as the failed machine.  If I do it this way the only down time is restoring the image.  Which I guess would be a few hours start to finish.  Also I guess there is a potential to lose some mail between the backup the night before and the failure.

Seems like this should be an easy thing.  Install Exchange on a server and click a box to say I want this to synchronize with server2.  Wishful thinking I guess.
Simon Butler (Sembee)ConsultantCommented:
Two servers with a DAG will give you what you need. You will need to ensure that DNS is setup correctly. In the event of a failover the DNS entry for the server will need to be changed to the second server. If you want that bit to be automated then you will need to use a load balancer.

The image method isn't really going to work because Exchange is a "living" product. It constantly changes. If you take an image now, within 30 seconds it is out of date and you are at risk of data loss.


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