Exchange 2010 high availability on a budget

AJNS used Ask the Experts™
I have a small customer running Exchange 2010 who are looking for some high availability. They are a small shop with 30 users. However they can not work when Exchange goes down. It is their email program, their calendars and they integrate document management and time tracking into Outlook.

They essentially come to a standstill if Exchange goes offline, they are highly reliant on technology. But because of the small size the budget is not unlimited. So I need some suggestions for Exchange high availability on a budget.

The software is Exchange 2010 running on 2008 R2 Standard at the moment. That rules out a DAG so changes have to be made.

I believe the options are to keep 2010 but upgrade 2008 R2 to enterprise so we can do DAG's. Or upgrade to 2012 R2 to do DAG's. Keeping Exchange at 2010 saves some money and 2013 does not really have any features they need unless there is a compelling feature related to high availability.

The hardware currently is a number of HP servers but that is going to be upgraded to bigger HP servers running either vmware or hyper-v so I can have more flexibility with adding servers. All storage will be local storage, no SAN here.

So what is the minimum number of copies of Exchange I need to make this highly available?

My thoughts are at least 3. Two running the MBX role in a DAG and one acting as the CAS server. But if the CAS server goes down it won't matter that the DAG is up. So I guess it's 4 servers. Two running MBX in a DAG and 2 running CAS in an array.

Or is there a way to have just 2 servers each of them running all roles? They act as a DAG and as a CAS array. Not sure that is possible.

Any other scenarios here that make more sense or suggestions on how to make these two options work?

Any help is appreciated.
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Jeffery HayesSystem Support Technician

For the best bang for your buck you should look into Office 365. They have a vast array of options for price and can help you get setup with High-Availability for cheap.

Here is a good article from Tech-Net for understanding the factors needed for HA. 

You can setup both a CAS Array, and a Dag on two, but then what about your Hub Transport Servers?

Honestly look at Office 365 if it's only 30 people as they have cheap options.


I should have mentioned that office365 as well as any hosted solution is not an option. 365 because we are in Canada and the client will not have data sitting in Microsoft's US data centers. That's a discussion of it's own but they are lawyers and won't do it so that's a no go.

Hosting even in Canada is out because of the way their document management and time tracking works. Both vendors do not support hosted solutions. A colleague of mine tried it and it's not pretty.

I have to work within their framework. That's why this is challenging, they don't fit inside a neat and tidy box. If I followed Microsoft's guidance they would be on Small Business Server or 365 but that's not a fit for them. They have a small firms budget but a big companies needs.

Thanks for bringing up Hub Transport. I hadn't put much thought into that one. My understanding was they are fault tolerant just by adding the role to multiple servers as long as the send/receive connectors are setup.
System Support Technician
Yes they should be fault tolerant, as they have shadow queues as well. Leave it to Lawyers to make things a pain.

I'd go with the option of having 3 servers for each role. If your doing Hyper-V and have the resources make 3 Dag's, 3 Cas arrays, and 3 MBX Roles.

I mean only 30 users shouldn't require too much resources.

Then of course you still need your DC and your FMSO Roles.
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I have mine dags setup on just 2 servers. both have all roles(except edge)
I also have a mail appliance in both sites. if 1 exchange goes down the other picks up..if 1 smarthost goes sends to the other
Adam BrownSenior Systems Admin
Top Expert 2010
Probably your cheapest bet for HA would be VM Host level HA. This would allow you to remain operable if one physical server failed. You could replicate a VM between Virtual Server Hosts (Hyper-V supports this natively for free in Server 2012) and if one host fails the VM running exchange will go to the other server and keep things from failing. This would require two Windows 2012 licenses and 1 Exchange server license, as well as hardware for the two physical servers.

Anything beyond that would require at least 3 Exchange Server licenses to allow Database high-availability and protection against database Corruption. For instance, you can have 3 VMs, with 1 CAS/HUB and 2 MBX servers, This will allow you to have a Lagged copy of your databases on each MBX server so if the running database gets corrupted, you can roll back in time up to 14 days. The Single CAS server is all you need to provide high-availability for that roll if you run these on VMs and have them replicate between Host servers, kind of like the above.

You can also have two VMs running all the roles with a lagged DAG, but this configuration requires a Hardware Load Balancer configured to balance traffic between the two CAS/HUB roles, since windows NLB isn't available to you in this configuration. If you have this configuration, failure on the primary CAS server will require you to change DNS/routes to point users to the secondary CAS server. If you only have 1 CAS/HUB server, you don't have to worry about that and you'll have some high availability with VM failover in the mix, but you can usually get a simple but effective load balancer for less than the cost of an Exchange License, so this may be the best option.


Sorry for the delay, I was doing a little more research.

Jefferey - You said three servers for each role. Curious why three.

acbrown2010 - I'm not familiar with Host Level HA. I did a little research and it sounds like it could work. In a way it almost sounds too good to be true. If it works as advertised why run any type of dag or cluster?

Maybe it's just because I'm not familiar with it but it creates a lot of questions for me. Do you really only need one Exchange license for this? If the host dies how does the other host know to bring up the guest with Exchange and how old is the data in Exchange? I assume the downtime would be the same if you simply rebooted exchange. One goes off and the other comes on after booting.

I also see that it relies on shared storage. Do you know if it will use local storage?

For your other comments I've looked into a load balancer for the CAS array from Barracuda and the price is not that bad. If it allows me to run a CAS array on the same servers as my DAG's then it saves me exchange licenses and hardware costs.
Adam BrownSenior Systems Admin
Top Expert 2010
Host level HA relies on the high availability features of the virtualization software you use. The downside to it is if there is a software failure or database corruption it can't recover automatically. It does require shared storage though, unlike DAG. It will work with ISCSI or similar sans. Server 2012 has some features in hyperv that will allow you to have psuedo high availability through direct VM replication. If one server fails you can start the vm on the other server if you use replication.

To answer your question to jefferey, a three node DAG will allow you to have a third, lagged copy of the database to protect against db corruption. However, even with that you don't need three servers gor each role, particularly if you use a load balancer. MS does not recommend using windows NLB, so you will want to get a load balancer no matter what.


I think even a "cheap" SAN is going to be an issue for the budget. It's really hard to justify a SAN for 30 users.

Having a lagged database makes sense, that's why he suggested three.

I think this is what I am going to do.

For hardware I am going to purchase 2 new servers for running hyper-v and a hardware NLB.

I will purchase 2 copies of Server 2012 which with MS's licensing lets me run 2 copies of 2012 as guests on each server. Two of them will run exchange and two can be used for other uses. I will purchase 2 more copies of Exchange (2013 downgraded to 2010). Saves me buying CAL's.

I will install Exchange with all roles on both servers creating a CAS array utilizing the hardware NLB and a DAG with active - active. Once that is in place and working I can wipe the current exchange server. That hardware is fairly new. I can then install exchange on there and use it as the passive db in the DAG.

I think that gives me the most bang for my buck and provides the best high availability.

Anybody want to poke holes in that and tell me what I'm doing wrong or what I could do better?

Appreciate all feedback.


Not sure why this wasn't closed, I'm sure I entered these points a long time ago. Anyway, I awarded points based on not just the "correct" answer but also because there was good information as I believe there was no one right answer to this.


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