There are several Business Continuity Clustering deployment scenarios that can be used to achieve the desired level of disaster recovery. Three possible scenarios include:
The two-site business continuity cluster deploys two independent clusters at geographically separate sites. Each cluster can support up to 32 nodes. The clusters can be designed in one of two ways:
Active Site/Active Site: Two active sites where each cluster supports different applications and services. Either site can take over for the other site at any time.
Active Site/Passive Site: A primary site in which all services are normally active, and a secondary site which is effectively idle. The data is mirrored to the secondary site, and the applications and services are ready to load if needed.
The active/active deployment option is typically used in a company that has more than one large site of operations. The active/passive deployment option is typically used when the purpose of the secondary site is primarily testing by the IT department. Replication of data blocks is typically done by SAN hardware, but it can be done by host-based mirroring for synchronous replication over short distances up to 10 km.
Figure 1-3 shows a two-site business continuity cluster that uses storage-based data replication between the sites. BCC uses eDirectory and Identity Manager to synchronize cluster information between the two clusters.
Figure 1-3 Two-Site Business Continuity Cluster
The multiple-site business continuity cluster is a large solution capable of supporting up to four sites. Each cluster can support up to 32 nodes. Services and applications can do fan-out failover between sites. Replication of data blocks is typically done by SAN hardware, but it can be done by host-based mirroring for synchronous replication over short distances up to 10 km.
Figure 1-4 depicts a four-site business continuity cluster that uses storage-based data replication between the sites. BCC uses eDirectory and Identity Manager to synchronize cluster information between the two clusters.
Figure 1-4 Four-Site Business Continuity Cluster
Using additional software, all services, applications, and data can be rendered through the Internet, allowing for loss of service at one site but still providing full access to the services and data by virtue of the ubiquity of the Internet. Data and services continue to be available from the other mirrored sites. Moving applications and services to the Internet frees corporations from the restrictions of traditional LAN-based applications. Traditional LAN applications require a LAN infrastructure that must be replicated at each site, and might require relocation of employees to allow the business to continue. Internet-based applications allow employees to work from any place that offers an Internet connection, including homes and hotels.
The low-cost business continuity cluster solution is similar to the previous two solutions, but replaces Fibre Channel storage arrays with iSCSI storage arrays. Data block mirroring can be accomplished either with iSCSI-based block replication, or host-based mirroring. In either case, snapshot technology can allow for asynchronous replication over long distances. However, the low-cost solution does not necessarily have the performance associated with higher-end Fibre Channel storage arrays.