Exchange 2007 comes with 4 types of clustering high availability features!!! No doubt CCR being the favorite among admins nowadays… Decide on your own !!!
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. We enable LCR on the same server, but on a different physical drive. The whole point in enabling LCR is to have a copy of the database and logs if the disk subsystem which holds the same crashes.
Cluster Continuous Replication (CCR): 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. An exchange organization having CCR will have copies of the database and log files on a target server which acts as a passive node.
Standby continuous replication (SCR): SCR is a new feature introduced in Exchange 2007 SP1. 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. The main objective of configuring SCR is the high availability it delivers. If an entire site is down, we can use the Restore-StorageGroupCopy cmdlet to enable the Standby Cluster in the other site.
Single-Copy Clusters (SCC): 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 clusters are basically the same as traditional clusters in early versions of Exchange, with some improvements in Exchange 2007.
CCR is the recommended technology for Hosted Messaging and Collaboration version
A Comparison of the Different High Availability Solutions
The following table lists the difference between LCR, CCR and SCC in Exchange 2007.
Issue LCR CCR SCC
Failure or planned downtime of one node No protection Protected Protected
Database corruption Probable protected if database corruption is not replicated to the copy Probable protected if database corruption is not replicated to the copy No protection
Failed local storage system Protected if second copy is on a different storage system Protected Protected if the failure is isolated to one node
Failed disk subsystem Probable protected if second copy is on a different storage system Protected No protection
Data center failure No protection Probable protected if the second node is located in a second datacenter and the file share witness is accessible by it No protection
Utilizes Windows clustering No Yes Yes
Can use low cost storage systems Yes Yes No
Storage requirements Double Double Single
Backup databases without impacting server Partial if the second copy is located on a different storage system the impact will be less. With CCR the primary server is not affected at all. Yes No