what is split brain in oracle rac

In simple terms Split brain means that there are 2 or more distinct sets of nodes, or cohorts, with no communication between the two cohorts. Also, for large data centers with a need to support many applications with Oracle Data Guard requirements, you can build an Oracle Data Guard hub to reduce the total cost of ownership. Although traditional solutions (such as backup and recovery from tape, storage-based remote mirroring, and database log shipping) can deliver some level of high availability, Oracle Data Guard provides the most comprehensive high availability and disaster recovery solution for Oracle databases. If your business does not require the scalability and additional high availability benefits provided by Oracle RAC, but you still need all the benefits of Oracle Data Guard and cold cluster failover, then Oracle Database with Oracle Clusterware and Oracle Data Guard is a good compromise architecture. The goal of the MAA is to remove the complexity in designing the optimal high availability architecture by providing configuration recommendations and tuning tips to optimize your architecture and Oracle features. However, when the data centers are located more than 66 kilometers apart, you must use a series of repeaters and converters from third-party vendors. Split Brain Condition occurs when a single cluster has a failure that results in reconfiguration of cluster into multiple partitions, with each partition forming its own sub-cluster without the knowledge of the existence of other. Similar to using Oracle Data Guard in SQL Apply mode, Oracle GoldenGate can capture database changes, propagate them to destinations, and apply the changes at these destinations. Oracle Enterprise Manager support for patch application simplifies software maintenance. Different character sets are required between the primary database and its replicas. Nodes 1,2 can talk to each other. Additional protection from data center failure with special considerations that are documented in Section 7.1.4.1, Highest level of availability for server or computer room failure. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). Prior to Oracle Database 12.1.0.2c, the algorithm to determine the node (s) to be retained / evicted is as follows: If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster . (adsbygoogle=window.adsbygoogle||[]).push({}); Split Brain is often used to describe the scenario when two or more nodes in a cluster, lose connectivity with one another but then continue to operate independently of each other, including acquiring logical or physical resources, under the incorrect assumption that the other process(es) are no longer operational or using the said resources. Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard, The application servers on the secondary site are connected to the WAN traffic manager by a dotted line to indicate that they are not actively processing client requests at this time. Better suited for WANsRemote mirroring solutions based on storage systems often have a distance limitation due to the underlying communication technology (Fibre Channel or ESCON (Enterprise Systems Connection)) used by the storage systems. What is Voting Disk & Split Brain Syndrome in RAC Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. Maximum RTO for instance or node failure is in seconds. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. You can achieve the highest level of availability when using Oracle RAC and Oracle Data Guard and there is no need to make application changes to use these Oracle Database features. The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. Oracle Secure Backup provides a centralized tape backup management solution. Oracle Application Server provides high availability and disaster recovery solutions for maximum protection against any kind of failure with flexible installation, deployment, and security options. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. Split Brain Condition - STOMITH STONITH fencing - dba-oracle.com But 1 and 2 cannot talk to 3, and vice versa. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. Customer can designate which server(s) and resource(s) are critical 2. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. Oracle Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. Rolling upgrade for system, clusterware, database, and operating system. Oracle Net Services provide client access to the Application/Web server tier at the top of the figure, Figure 7-4 Oracle Database with Oracle RAC Architecture. Online Reorganization and Redefinition allows for dynamic data changes. Simulate loss of connectivity between two nodes. Because Oracle Data Guard only propagates the redo data in the logs, and the log file consistency is checked before it is applied, all such external corruptions are eliminated by Oracle Data Guard. This is called Split Brain. To maintain the standby site for failover, not only must the standby site contain homogeneous installations and applications, data and configurations must also be synchronized constantly from the production site to the standby site. The following list describes examples of Oracle Data Guard configurations using multiple standby databases: A world-recognized financial institution uses two remote physical standby databases for continuous data protection after failover. The data is derived from actual user experiences and from Oracle service requests. If all the sub-clusters are of the same size, the functionality has been modified as: If the sub-clusters have equal node weights, the sub-cluster with the lowest numbered node in it survives so that, in a 2-node cluster, the node with the lowest node number will survive. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. Split Brain Syndrome Basic Concept in Oracle RAC Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. If the observer is unable to regain a connection to the primary database within the specified time, and the target standby database is ready for fast-start failover, then fast-start failover ensues. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. Oracle Clusterware provides a number of benefits over third-party clusterware. For example, if a stray write occurs to a disk, or there is a corruption in the file system, or the host bus adaptor corrupts a block as it is written to disk, then a remote mirroring solution may propagate this corruption to the disaster-recovery site. The high availability benefits to using Oracle RAC One Node include the following: Offers better database availability than traditional cold failover solutions, Provides better virtualization for databases than hypervisor-based solutions, Enables online migration of database instances and online patching and upgrading of operating system and database software (incurring no downtime), Delivers a comprehensive, single-vendor solution, with no need to implement third-party products, Is ready to scale and upgrade to multinode Oracle RAC, Provides a standardized environment and a common toolset for both single-node and multinode Oracle database deployments, Is less expensive than cold fail over solutions or a full Oracle RAC deployment. The center frame shows the configuration during fast-start failover. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. Although both types of solutions provide high availability, active-active solutions generally offer higher scalability and faster failover, although they tend to be more expensive. PDF Oracle Clusterware 12c Release 2 Technical Overview The premise of the Data Guard hub is that it provides higher utilization with lower cost. Fast Recovery Area manages local recovery-related files. Oracle RAC on an extended cluster provides greater availability than a local Oracle RAC cluster, but an extended cluster may not completely fulfill the disaster recovery requirements of your organization . CSSD process in each RAC node maintains a heart beat in a block of size 1 OS block in a specific offset by read/write system calls (pread/pwrite), in the voting disk. Node Weighting for Split Brain Resolution Without better understanding of what is critical or of higher priority to the customer's workload, Oracle Clusterware has always resolved split brain conditions in favor of the cluster cohort containing the node with the lowest node number (i.e. The system resources can be dynamically allocated and deallocated depending on various priorities. In such a scenario, integrity of the cluster and its data might be compromised due to uncoordinated writes to shared data by independently operating nodes. The individual nodes are running fine and can accept user connections and work . For example : This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. (The application server on the secondary site can be active and processing client requests such as queries if the standby database is a physical standby database with the Active Data Guard option enabled, or if it is a logical standby database.). Database scalability beyond one instance or node. If your VM is sized too small, you can migrate the Oracle RAC One instance to another larger Oracle VM node in the cluster (using the online database relocation utility) or move the Oracle RAC One instance to another Oracle VM node, and then resize the Oracle VM.

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