Over the years Microsoft Exchange has added features to provide high availability for the mailbox database role. The latest version Exchange 2010 includes a feature named Database Availability Groups (DAG) that is similar to the Continuous Cluster Replication feature of Exchange 2007 but with greater flexibility. In particular, DAG doesn’t need to be specified during installation and can be configured after installing. In addition, Exchange 2010 servers that are members of DAGs can contain replicas of mailbox databases of each other, allowing us to make better use of server resources. We can also configure the Client Access and Hub Transport roles on the same server as the Mailbox servers that participate in the DAG. So conceivably we can configure a high availability solution for all Exchange roles using only two Exchange servers. If set up like this we will need to have an additional Windows 2008 server that will be configured as a file share witness to establish a quorum for the cluster. Facebook
One additional noteworthy item is that the DAG feature is available for use with Exchange 2010 Standard Edition. This is unlike with previous editions of Exchange where the Enterprise Edition was required to utilize high availability mailbox database solutions involving more than one server. To make use of DAG Windows 2008/2008 R2 Enterprise Edition is required for the Exchange servers, however.
In this example I have configured three servers, all running Windows 2008 R2. One is a domain controller that will act as the file share witness. In a production environment it is recommended to configure the file share witness on a domain member server, it is not desirable to use a DC because additional access permissions need to be granted on the file share witness and doing so on a DC makes AD less secure. Both of my Exchange 2010 servers (EXCH11 & EXCH12) are configured with 2 NICs for redundancy of replication and heartbeat traffic. In addition, I will configure 2 additional hard drives for each Exchange server that will contain the Exchange log and database files.
Preconfiguring and Installing Exchange Servers (EXCH11 & EXCH12)
Open up the Network Connections on both servers.
I have label the two interfaces, the LAN interface is the main NIC that connects to the rest of my network. Right click Heartbeat and choose Properties.
Today I’m going to walk you through the set up of an open source email gateway on CentOS 5.4. Some of the tools we’ll use include Postfix, SpamAssassin, ClamAV, MailScanner, and MailWatch.
First let’s install some prerequisites from the CentOS base packages:
# yum install wget ntp vixie-cron crontabs postfix patch rpm-build binutils glibc-devel gcc make yum-protectbase yum-priorities
Next we’ll disable SELinux. I generally disable this on servers but you may want to keep it turned on if security is more of a concern. To disable, edit /etc/selinux/config and modify the parameter to read:
Reboot the server and log back in.