Single Copy Cluster: Server Redundancy in Software

Encoder QR Code in Software Single Copy Cluster: Server Redundancy

Single Copy Clusters (SCCs) can be thought of as Exchange clusters as we know them from previous versions of Exchange Server They use shared storage, which becomes a single point of failure out of the box, unless augmented by third-party solutions that provide redundancy to the storage As such, SCC provides the benefit of server redundancy, but does not provide any storage or database redundancy Failure of shared storage particularly the SAN and NAS variety that comes with plenty of redundancy built in, depending on the implementation is not very common However, it is a risk nevertheless that needs to be understood and mitigation steps taken

Part VI:

Another important factor to keep in mind is the comparatively more stringent hardware requirements for SCC hardware used for nodes of a cluster should be similar, and the entire solution should be listed in the Cluster Solution category on the Windows Server Catalog of Tested Products Together, these requirements drive up the cost of high availability and may affect your choice of the type of clusters to deploy With that out of the way, Single Copy Clusters do have some notable features lacking in the CCR model, including the ability to scale up beyond the two-node limitation of CCR, to as many as eight nodes on both Windows Server 2003 and Windows Server 2008 Organizations with significant investments in expensive, redundant storage, and perhaps third-party solutions in use to provide replication and geographically dispersed clustering solutions, may find it beneficial to stick with this known model If you decide to take this route, make sure the existing solutions are compatible with Exchange Server 2007, and determine whether any upgrades are required for compatibility SCC benefits from Exchange Server 2007 s reduced number of cluster resources remember, there is no support for any other server role except the Clustered Mailbox Server There are no equivalents of protocol virtual server resources such as HTTP, SMTP, POP3, and IMAP The only resources exposed by Exchange Server 2007 are System Attendant, Information Store, and Exchange Database instances, in addition to the Network Name and IP Address resources that must exist in a CMS This adds to the simplification of the cluster resource dependency model, resulting in faster failovers in most deployments

are shared volumes on which Exchange Server 2007 databases and transaction logs reside Additionally, the Cluster group may use the traditional shared quorum resource, or the quorum may reside locally on each node if the Majority Node Set quorum is used, or optionally the MNS quorum with a File Share Witness may also be used for SCC

Cluster Continuous Replication (CCR) is the brave, new child of Exchange Server 2007 s high availability bandwagon It uses Windows Server s Cluster Service and provides the same automated failover capabilities that have characterized Exchange clusters since we have known them However, in addition to providing server redundancy, it also provides storage redundancy Gone is the requirement of using shared storage, which forced one to use the kludgy parallel/shared SCSI that many administrators shied away from in the past, or more expensive NAS/SAN storage that became the de facto clustering requirement and made Exchange clusters quite attractive to the bottom line of storage companies Following are some of the notable benefits of CCR: CCR does not require shared storage; local/direct attached storage can be used CCR uses Exchange Server 2007 s continuous replication technology to replicate transaction logs from an active node to the passive node In addition to server redundancy, CCR provides storage and database redundancy out of the box If one server becomes unavailable, or its storage fails completely, a Clustered Mailbox Server using CCR will fail over, survive, and continue to provide service Besides its replication features, it capitalizes on Windows Server s Majority Node

19: