Implementing Multi-Site Clusters April Trần Văn Huệ Nhất Nghệ CPLS

Overview of Multi-Site Clusters What Are Multi-Site Clusters? What Makes Multi-Site Clusters Unique? Why Use a Multi-Site Cluster? Evaluating the Business Need for a Multi-Site Cluster Storage Challenges for Multi-Site Clusters Synchronous / Asynchronous Replication? Network Challenges for Multi-Site Clusters Choosing the Appropriate Quorum Mode in Multi-Site Clusters Demo: Deploying a Multi-Site Cluster Agenda:

What Are Multi-Site Clusters? A multi-site cluster is a cluster that has been extended so that different nodes in the same cluster reside in separate physical locations Site A Site B SAN

What Makes Multi-Site Clusters Unique? Multiple storage arrays, which are independent in each site Nodes commonly access storage local to their own sites Storage is replicated between sites No “true” shared disk is visible to all nodes Site A Site B Changes are made on Site A and replicated to Site B Replica

Why Use a Multi-Site Cluster? Advantages over cold standby server in a disaster recovery site: Automatic failover Reduced downtime Lower complexity Reduced administrative overhead Automatic synchronization of application and cluster changes Better service continuity than cold standby servers Reduced human error factor Reduced reliance on old, potentially error-prone procedures

Evaluating the Business Need for a Multi-Site Cluster Because of increased cost and complexity, multi-site clusters aren’t for every company or application Evaluate the application type and importance, and consider available alternatives Plan for the application and hardware architecture, and for routine failover and failback testing

Storage Challenges for Multi-Site Clusters ChallengeDescription Requires a separate or third-party data replication solution Hardware (block level) storage-based replication Software (file system level) host-based replication Application-based replication (such as Exchange 2007 Cluster Continuous Replication) Can be either synchronous or asynchronous replication Synchronous: No acknowledgement of data changes made in Site A until the data is successfully written to Site B Asynchronous: Data changes made in Site A will eventually be written to the storage in Site B

What Is Synchronous Replication? When you use synchronous replication, the host receives a “write complete” response from the primary storage after the data is written successfully to both storage locations Primary Storage Secondary Storage Write Request Write Complete Replication Acknowledgement Data Site A Site B

What Is Asynchronous Replication? When you use asynchronous replication, the host receives a “write complete” response from the primary storage after the data is written successfully on the primary storage Primary Storage Secondary Storage Write Request Write Complete Replication Data Site A Site B

Comparing Synchronous and Asynchronous Replication Replication TypeDescription Synchronous Works across shorter distances Results in no data loss Requires high-bandwidth/low-latency connections Allows write latencies to impact performance AsynchronousStretches over longer distances Results in potential data loss on hard failure Assumes large enough bandwidth to keep up with data Does not significantly impact performance

Network Challenges for Multi-Site Clusters Inter-node communications are time sensitive; you might need to configure these thresholds to meet the higher WAN latency DNS replication might impact client reconnect times when failover is based on hostname Some applications might require all of the nodes to be in the same Active Directory site Active Directory replication latency might effect application data availability

Choosing the Appropriate Quorum Mode in Multi-Site Clusters Quorum ModeChoose when: Node and Disk Majority Directed by vendor only No Majority: Disk Only Directed by vendor only Node Majority Limited to two sites Node and File Share Majority Three sites are available

Using Node and File Share Majority in a Multi-Site Cluster File share witness allows a 2-node cluster with no shared disk Single file server can serve as the witness for multiple clusters Third-Party Replication Mechanism Site C File Share Witness SAN Site A Site B SAN WAN

Deploying a Multi-Site Cluster When deploying multi-site clusters: Ensure that the business requirements are met by the solution Use a hardware vendor to create a full solution for multi-site clusters Choose the correct quorum mode to properly maintain functionality in the event of failures Choose the correct storage replication solution to meet these needs

Demo Demo: Multi Site Cluster

Demo Private network: /16 Public network: /24 PC08: DC, Quorum IP: Datakeeper replicate PC09: IP: IP: PC10: IP: IP: Site 1 Site 2 Site 3