With the release of Exchange Server 2007 Microsoft introduced some exciting new high availability options. Service Pack 1 for Exchange Server 2007 introduced yet another high availibity option.
Looking at the question we recieved at the Exchange Server 2007 booth at TechEd 2008 IT Pro in North America, it appears it’s not clear to everyone what solution to choose with regards to the intended result.
Although the TLA’s (Three Letter Acronyms) might appear challanging, they make perfect sence if you see what they stand for and what the specific solution does for you with regards to Exchange Server 2007 High Availibility.
Local continuous replication (LCR) LCR is a single-server solution that uses built-in asynchronous log shipping 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 storage group. LCR provides log shipping, log replay, and a quick manual switch to a secondary copy of the data. Be sure to understand that this solution is primarily intended to give you an up-to-date copy of the database on the same server as the original database. It will NOT automatically fail over in case you loose or corrupt your primairy database.
Cluster continuous replication (CCR) CCR, which is a non-shared storage failover cluster solution, is one of two types of clustered mailbox server (CMS) deployments available in Exchange 2007. CCR is a clustered solution (referred to as a CCR environment) that uses built-in asynchronous log shipping technology to create and maintain a copy of each storage group on a second server in a failover cluster. CCR is designed to be either a one or two data center solution, providing both high availability and site resilience. CCR is very different from clustering in previous versions of Exchange Server. CCR will give you automatic failover in case of a disaster. To the end-user all nodes in the cluster appear to be a single server. So in case of a disaster, you do not have to reattach mailboxes to users or anything like that.
Standby continuous replication (SCR) SCR is a new feature introduced in Exchange 2007 SP1. As its name implies, SCR is designed for scenarios that use or enable the use of standby recovery servers. SCR extends the existing continuous replication features and enables new data availability scenarios for Exchange 2007 Mailbox servers. SCR uses the same log shipping and replay technology used by LCR and CCR to provide added deployment options and configurations by providing the administrator with the ability to create additional storage group copies. SCR can be used to replicate data from stand-alone Mailbox servers and from clustered mailbox servers. So this option is about the same as LCR, except that you can ‘send’ your storage group/mailbox store copy to another server. This is ideal for scenarios where you have to recover from a complete site failure. You can take SCR copies of active CCR clusters. After a site failure, where the primary site is now gone and the CCR cluster in the primary site is no longer alive, you can make your SCR copy the active copy and set up CCR at the second site!
Single copy clusters (SCC) SCC, which is a shared storage failover cluster solution, is the other of two types of clustered mailbox server deployments available in Exchange 2007. SCC is a clustered solution that uses a single copy of a storage group on storage that is shared between the nodes in the cluster. SCC is somewhat similar to clustering in previous versions of Exchange Server; however, along with numerous improvements, there are also some significant changes. This SCC option can be compare to the ‘old’ Exchange 2000/2003 clustering technology.
Hopefully this quick overview will help you in deciding which option to choose. Remember that you can combine certain replication techniques to create even more redundancy.