However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. The common voting result will be: a. Footnote3For qualified one-off patches only. host02 is retained as it has higher number of database services executing. Run-time performance level management with Oracle Database Quality of Service Management (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)), Zero downtime with Grid Control provisioning, Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patchesFoot1, Database Grid with site failure protection, Simplest high availability, data protection, and disaster-recovery solution, Automatic and fast failover for computer failure, storage failure, data corruption, for configured ORA- errors or conditions and database failures, Rolling upgrade for system, clusterware, database, and operating systemFoot2, Ability to off-load backups to the standby database, Ability to off-load read and reporting workload to the standby database. To simulate loss of connectivity between two nodes, stop the private network service on one of the nodes: Verify that host01 is retained as it has a lower node number and host02 is evicted: To simulate loss of connectivity between two nodes, stop private network service on one of the nodes: Verify that host02 is retained as it has higher number of database services executing and host01 is evicted although it has a lower node number: If the sub-clusters are of the different sizes, the functionality is same as earlier, i.e. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). Figure 7-5 shows an Oracle RAC extended cluster for a configuration that has multiple active instances on six nodes at two different locations: three nodes at Site A and three at Site B. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. It is possible, under certain circumstances, to build and deploy an Oracle RAC system where the nodes in the cluster are separated by greater distances. For data resident in Oracle databases, Oracle Data Guard, with its built-in zero-data-loss capability, is more efficient, less expensive, and better optimized for data protection and disaster recovery than traditional remote mirroring solutions. Logical or user failures that manipulate logical data (DMLs and DDLs). The individual nodes are running fine and can accept user connections and work . This configuration consists of a central resource supporting 10 applications and databases in the grid, rather than managing 10 separate system or storage units in a nongrid infrastructure. Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect, Although the servers are physically up and running and the database instances on these servers is also running. Then there are two cohorts: {1, 2} and {3}. Table 7-3 identifies the additional capabilities provided by the architectures that build on Oracle Database and attempts to label each architecture with its greatest strengths. 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. Oracle recommends that you create and store the local backups in the fast recovery area. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. Oracle Application Server instances can be installed in either site as long as they do not interfere with the instances in the disaster recovery setup. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). Fast Recovery Area manages local recovery-related files. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. You can define multiple application VIPs, with generally one application VIP defined for each application running. Start both the services for database admindb so that equal number of database services execute on both the nodes. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. With Oracle Clusterware, . The fast-start failover has completed and the target standby database is running in the primary database role. The problem which could arise out of this situation is that the sane . Starting in Oracle Database 12.1.0.2c, the new algorithm to determine the node(s) to be retained / evicted is as follows: Now I will demonstrate this new feature in an Oracle 12.1.0.2c standard 3 node cluster, using an RAC database called admindb for one of the possible factors contributing to the node weight, i.e. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. These best practices are required to maximize the benefits of each architecture. Split Brain Syndrome in RAC. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. Oracle Data Guard is a high availability and disaster-recovery solution that provides very fast automatic failover (referred to as fast-start failover) in database failures, node failures, corruption, and media failures. If the primary system should fail, the first standby database becomes the new primary database. More investment and expertise to build and maintain an integrated high availability solution is available. Oracle Automatic Storage Management and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and utilization. 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. An infrastructure services provider to the telecommunication industry uses a single standby database located over 400 miles away from the primary database configured for synchronous redo transport, enabling zero-data-loss failover for maximum data protection and high availability. With the snapshot standby database hub, you can use the combined storage and server resources of a grid instead of building and managing individual servers for each application. Footnote8With automatic block repair, this should be the most common block corruption repair. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. If the fast recovery area is on the source volume that is remotely mirrored, then you must also remotely mirror the flashback logs. Oracle Security Features prevent unauthorized access and changes. New requests are accepted after the Split-Brain event and then performed on potentially corrupted system state (thus potentially corrupting system state even further). Footnote2Oracle ASM automatically rebalances stored data when disks are added or removed while the database remains online. The term "Split-Brain" is often used to describe the scenario when two or more co-operating processes in a distributed system, typically a high availability 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 . The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. Maximum RTO for instance or node failure is in seconds. When a node is physically up and running and database instances are also running fine, but private interconnect fails between two or more nodes and an . Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). Then there are two cohorts: {1, 2} and {3}. An exception is undropping a table, which is literally instantaneous regardless of detection time. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. This architecture is identical to the single-standby database architecture that was described in Section 7.1.5.1, except that there are multiple standby databases in the same Oracle Data Guard configuration. For example, for a business that has a corporate campus, the extended Oracle RAC configuration could consist of individual Oracle RAC nodes located in separate buildings. After you have chosen an architecture, then implement it using the operational and configuration best practices described in the MAA white papers and in Oracle Database High Availability Best Practices. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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. Now talking about split-brain concept with respect to oracle . The group(cohort) with more cluster nodes survive Oracle Data Guard is designed so that it does not affect the Oracle database writer (DBWR) process that writes to data files, because anything that slows down the DBWR process affects database performance. Oracle Data Guard is operating in a steady state, with the primary database transmitting redo data to the target standby database and the observer monitoring the state of the entire configuration. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. For example, you can put the files on different disks, volumes, file systems, and so on. Q39) Mention what is split brain syndrome in RAC? host01 is retained as it has a lower node number. Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. But 1 and 2 cannot talk to 3, and vice versa. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. 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 . For example : The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. Traditionally, Oracle RAC is used in a multinode architecture, with many separate database instances running on separate servers. Filed Under: oracle, RAC Tagged With: RAC, split brain, vcs basics Communication faults, jeopardy, split brain, I/O fencing, How to Enable or Disable Veritas ODM for Oracle database 12.1.0.1, ORA-16713: The Oracle Data Guard broker command timed out When Changing LogXptMode, Managing Oracle Database Backup with RMAN (Examples included), Cron Script does not Execute as Expected from crontab Troubleshoot, Oracle SQL Script to Report Tablespace Free and Fragmentation, Beginners Guide to Flash Recovery Area in Oracle Database, How to Identify the Last and Next Refresh Dates for a Materialized View, Oracle 20c New Feature: PDB Point-in-Time Recovery or Flashback to Any Time, How to use nomodeset to Troubleshoot Boot Issues. Oracle Secure Backup provides a centralized tape backup management solution. Rolling upgrade for system, clusterware, database, and operating system. For example, if the primary database fails over to one of the standby databases in the Data Guard hub, the new primary database acquires more system and storage resources while the testing resources may be temporarily starved. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. Oracle Enterprise Manager support for patch application simplifies software maintenance. 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. Prior to Oracle Database 12.1.0.2c, the algorithm to determine the node(s) to be retained / evicted is as follows: However, starting from 12.1.0.2c, in case of split brain, some improvement has been made to node eviction algorithm. An Oracle RAC database is connected to three instances on different nodes. Thus, we observed that when unequal number of database services are running on the two nodes, the node with higher number of database services survives even though it has a higher node number. With Oracle Clusterware, you also define an application VIP so that users can access the application independently of the node in the cluster where the application is running. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. 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. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Clients are connected to the logical standby database and can work with its data. The voting result is similar to clusterware voting result. To protect against site failures, the MAA recommends that Oracle RAC and Oracle Data Guard reside on separate systems (clusters) and data centers. Compared to mirroring, Oracle Data Guard provides better performance and is more efficient, Oracle Data Guard always verifies the state of the standby database and validates the data before applying redo data, and Oracle Data Guard enables you to use the standby database for updates while it protects the primary database. 2. In previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. Oracle Database High Availability Architectures, Choosing the Correct High Availability Architecture, Integrating Application Server High Availability, Integrating High Availability for All Applications. 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. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. What is split brain in Oracle RAC? What Is Oracle RAC. Maximum RTO for instance or node failure is in minutes. Different character sets are required between the primary database and its replicas. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. When you move the Oracle RAC One Node instance to the newly resized Oracle VM node, you can dynamically increase any limits programmed with Resource Manager Instance Caging. The center frame shows the configuration during fast-start failover. You can have up to 32 voting disks in your cluster. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware. Footnote4Database is still available, but a portion of the application connected to the failed system is temporarily affected. This architecture is the recommended configuration for Maximum Availability Architecture (MAA). Each instance is associated with a service: HR, Sales, and Call Center. 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. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. When two or more nodes fail to ping or connect to each other via this private interconnect, theclustergets partitionedinto two or more smaller sub-clusters each of which cannot talk to others over the interconnect. When the instance members in a RAC fail to ping/connect to each other via this private network and continue to process data block independently. Oracle Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. This is called Split Brain. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. Oracle Flashback Technology optimizes logical failure repair. Split Brain Syndrome, In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability, Automatic and fast failover for computer failure, Minimum rolling upgrade capabilities for system, clusterware, and operating systemFootref1, High availability, scalability, and foundation of server database grids, Automatic recovery of failed nodes and instances, Fast application notification (FAN) with integrated Oracle client failover, FAN with integrated Oracle client failover for pooled resources and third-party vendor middle tiers. Off-load read-only, reporting, testing and backup activities to the standby database. Site configurations are on heterogeneous platforms. If the sub-clusters have unequal node weights, the sub-cluster having the higher weight survives so that, in a 2-node cluster, the node with the lowest node number might be evicted if it has a lower weight. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. Use a physical standby database if read-only access is sufficient. In Oracle Database 11g Release 2 (11.2), Oracle RAC One Node or Oracle RAC is the preferred solution over Oracle Clusterware (Cold Cluster Failover) because it is a more complete and feature-rich solution. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. 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. Clients on the network experience a period of lockout while the failover occurs and are then served by the other database instance after the instance has started. Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect, Although the servers are physically up and running and the database instances on these servers is also running. You should adopt the MAA best practices to achieve the optimal recovery time and configuration. But i want to test it on a test environment in my view for that i need to fail or make the node's to lose connectivity with one another but then continue to . At a high level, Oracle Application Server local high availability architectures include several active-active and active-passive architectures for the OracleAS middle-tier and the OracleAS Infrastructure. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. The cold cluster failover solution with Oracle Clusterware provides these additional advantages over a basic database architecture: Automatic recovery of node and instance failures in minutes, Automatic notification and reconnection of Oracle integrated clientsFoot3, Ability to customize the failure detection mechanism. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. For physical standby databases, this solution: Supports very high primary database throughput. To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. Split Brain Syndrome: In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. Oracle Clusterware: Enables you to use an entire software solution from Oracle, avoiding the cost and complexity of maintaining additional cluster software. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. 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. Controlfile is used similarly to voting disk in clusterware layer to determine which instance(s) survive and which instance(s) evict. The advantages to using Oracle RAC on extended clusters include: Ability to fully use all system resources without jeopardizing the overall failover times for instance and node failures, Extremely rapid recovery if one site fails, All of the Oracle RAC benefits listed in Section 7.1.4. Figure 7-7 Oracle Database with Oracle Data Guard on Primary and Multiple Standby Sites, Oracle Data Guard Concepts and Administration for more information about the various types of standby databases and to find out what data types are supported by logical standby databases, Oracle Database High Availability Best Practices for configuration best practices, The "Managing Data Guard Configurations Having Multiple Standby Databases - Best Practices" white paper, and other Oracle Data Guard white papers at. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. 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. Oracle Data Guard Advantages Over Traditional Solutions. High availability solution with added data and disaster recovery protection. Run-time performance level management with Oracle Database Quality of Service Management (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)). Thus, when a failover occurs, you can prioritize the system resources to production activity and allocate new system resources in a grid for the standby database functions. This architecture is referred to as an extended cluster. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. If zero data loss is required with minimum performance impact on the primary database, then the best practice is to locate the secondary site within 200 miles of the primary database. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. The servers on which you want to run Oracle Clusterware must be running the same operating system.