Going cheap still has limits

Over the Thanksgiving holiday here in the US, I finally got a chance to catch up on a lot of the information on Database Availability Groups (DAG) and other neat new features in Exchange 2010.  I’ll get back to talking about earlier versions shortly, but one trend that got me thinking was that smaller organizations will be looking to use Ex2010 to get failover capability without clustering technologies and – therefore – at a lower cost.  The problem is that while you can implement DAG much less expensively than a traditional or CCR cluster, there are some severe limits you need to be aware of. 

Note: I will be attempting to keep everything very neutral in this article, but do keep in mind that I work for a High Availability/ Disaster Recovery solution provider (see notice below).

First, to spell out the Standard versus Enterprise versioning debate.  Yes, you can get DAG capabilities in the Standard version of Exchange 2010.  This means that you can create a DAG without the need for shelling out the extra cash for the Enterprise version of the Exchange Server software itself.  However, since DAG requires some of the components from Microsoft Failover Clustering, if you want to use DAG you must be on Server 2008 RTM or R2 Enterprise Edition.  So, in short, Exchange Standard is a yes, Windows Standard is a big no.

Also, keep in mind that each Exchange 2010 Server Standard may have no more than 5 databases on it.  There seems to be a good deal of confusion around that, but as has been quoted in Jim McBee's blog and other places, that doesn’t mean each Standard server can host 5 live databases.  It means that the total of both live and passive copies of databases housed on that server many not be more than 5.  So, if you want 1 live database on each of 4 servers, you can get away with Exchange 2010 Standard.  However, if you have 3 live databases on 2 servers, the Standard version is not enough to allow you to perform DAG on all databases, as that would make 3 live and 3 passive on each box, for a total of 6 per server.

One thing that is not limited is your ability to use any Client Access License (CAL) on any Exchange Server version you’d like.  Enterprise CAL’s run just fine on Exchange Standard, and vice-versa.  This means that end-users running on Standard can get nifty features without requiring you to upgrade to Exchange Enterprise.

So, smaller organizations may very well be able to use the Standard version of Exchange 2010 (but not Windows) in order to get DAG functionality for their databases and other higher-end feature sets.  Just keep in mind that there are still limitations on the Standard version, and avoid hitting those limits if you’re staying on Standard.