High Availability for Exchange Server 2007

High Availability for Exchange Server 2007

Circumstances such as component failure, power outages, operator errors, and natural disasters can affect a messaging system's availability. To help prevent against such circumstances, it is crucial that companies plan and implement reliable strategies for maintaining high availability. A highly available messaging system can save money by providing consistent messaging functionality to users.

Exchange Server 2007 has three main High Availability features: Single Copy Cluster (SCC), Local Continuous Replication (LCR) and Cluster Continuous Replication (CCR). Exchange 2007 SP1 has an additional feature named Standby Continuous Replication (SCR), which can be classified as a Disaster Recovery feature rather than a High Availability feature.

Local Continuous Replication (LCR)
Local continuous replication (LCR) is a single-server solution that uses built-in technology to create and maintain a copy of a storage group on a second set of disks that are connected to the same server as the production Mailbox Server. LCR provides asynchronous log shipping, log replay, and a quick manual switch to a copy of the data.

Cluster Continuous Replication (CCR)
Cluster continuous replication (CCR) combines the replication and replay features in Exchange 2007 with failover features in Microsoft Cluster services. CCR is a solution that can be deployed with no single point of failure in a single datacenter or between two datacenters. CCR provides several advantages over clustering in previous versions of Exchange Server and single copy clusters in Exchange 2007. This feature takes the new Exchange Server 2007 Log file shipping and replay features and combines them with the features that are available in a more traditional 2 node Windows 2003 active/passive cluster setup. A traditional 2 node active/passive cluster certainly has its benefits, but it also has one major drawback and that is you still have a single point of failure when it comes to the Data Storage. CCR overcomes this disadvantage by storing the Exchange Active Database and Passive Database on different storage devices.

Single Copy Clusters (SCC)
Single copy clusters (SCC), known as shared storage clusters in previous versions of Exchange Server, are present in Exchange 2007, with some significant changes and improvements. With SCC, all of the hardware, including the disks used for Exchange data, must be listed in the Cluster category of the Windows Server Catalog. With CCR, the disks used for Exchange databases are local to each system and are not controlled or failed over as part of the cluster.

SCC provides redundancy for the server, but not for storage. CCR provide redundancy with no single point of failure. CCR allows you to simplify backup administration and offload backup IO demands completely to the passive replica server.

Microsoft Exchange Disaster Recovery with Site Resilience

Microsoft Exchange Disaster Recovery with Site Resilience

Messaging services are mission-critical or business-critical to all organizations. If the messaging system is not available, productivity can be lowered, and business and revenue opportunities can be lost. Even though site resilience is only one means of Exchange Server Disaster Recovery, in this post, we are focusing on the site resilience part of the Exchnange 2007 Disaster Recovery strategy. Site Resilience is highly important for organizations with multiple offices in different locations and all offices are relying on the same Exchange Servers, which will be the typical setup involved in most of the organizations. Site resilience will be useful in situation where the Primary datacenter is down or lost connectivity for a long duration which is not acceptable for the business to go with out Email.

Exchange 2007 SP1 has a very much avaited feature, named Standby Continuous Replication (SCR), which was only available with third party products. In Exchang 2007 SP1, microsoft has intgrated the Disaster Recovery feature to the Microsoft Exchange product itself. By integrating the Site Resilience in Exchange Server itself, Administrators has the advantage of managing the Exchange Server disaster recovery with in Exchange Server framework and avoiding third party support overheads.

SCR allows you to replicate your Exchange database information from your production servers to a standby server that can be brought online should the production servers be lost. Although existing Exchange 2007 technologies such as Clustered Continuous Replication (CCR) offer high availability, site resilience is something currently best achieved via SCR.

SCR enables a separation of high availability and site resilience. For example, SCR can be combined with CCR to replicate storage groups locally in a primary datacenter (using CCR for high availability) and remotely in a backup datacenter (using SCR for site resilience).

Sources and Targets

The starting point for SCR is called the source, which is any storage group on any of the following:

• Stand-alone Mailbox server
• Clustered mailbox server in a single copy cluster (SCC)
• Clustered mailbox server in a CCR environment

The endpoint for SCR is called the target, and the target can be either of the following:

• Stand-alone Mailbox server that does not have LCR enabled for any storage groups
• A standby cluster, which is a failover cluster where the Passive Clustered Mailbox role is installed, but no clustered mailbox server (e.g., no Active Clustered Mailbox role) has been installed in the cluster

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