In a non-RAC Oracle database, a single instance accesses a single database. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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 Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. Oracle Secure Backup provides a centralized tape backup management solution. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. Oracle Database High Availability Best Practices for information about configuring Oracle Database 11g with Oracle RAC on extended clusters, White papers about extended (stretch) clusters and about using standard NFS to support a third voting disk on an extended cluster configuration at http://www.oracle.com/technetwork/database/clustering/overview/. Typically, this is not possible with remote mirroring solutions. 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. A logical copy configured and maintained using Oracle GoldenGate is called a replica, not a logical standby database, because it provides many capabilities that are beyond the scope of the normal definition of a standby database. Applications can easily mask failures to the end user. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. Oracle Flashback Technology optimizes logical failure repair. All of the business benefits of Oracle RAC and Oracle Data Guard. Online Reorganization and Redefinition allows for dynamic data changes. 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. It requires only a standard TCP/IP-based network link between the two computers. This architecture is referred to as an extended cluster. Split Brain Syndrome in RAC. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. 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. For example, you can put the files on different disks, volumes, file systems, and so on. In addition, allowing maintenance operations to occur on a subset of components in the cluster while the application continues to run on the rest of the cluster can reduce planned downtime. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. Controlfile is used similarly to voting disk in clusterware layer to determine which instance(s) survive and which instance(s) evict. Oracle Data Guard provides a compelling set of technical and business reasons that justify its adoption as the disaster recovery and data protection technology of choice, over traditional remote mirroring solutions. For example, you can use your favorite application query in the database check action. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). 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. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. Network & Disk Heartbeats | Oracle Database Internal Mechanism Oracle Database with Oracle RAC architecture provides the following benefits over a traditional monolithic database server and the cold cluster failover model: Flexibility to increase processing capacity using commodity hardware without downtime or changes to the application, Ability to tolerate and quickly recover from computer and instance failures (measured in seconds), Optimized communication in the cluster over redundant network interfaces, without using bonding or other technologies. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. Oracle recommends that you use automatic undo management with sufficient space to attain your desired undo retention guarantee, enable Oracle Flashback Database, and allocate sufficient space and I/O bandwidth in the fast recovery area. Then this process is referred as Split Brain Syndrome. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. The Oracle Application Server High Availability Guide describes the following high availability services in Oracle Application Server in detail: Process death detection and automatic restart. Evaluate logical standby databases if additional indexes are required for reporting purposes and if your application only uses data types supported by logical standby database and SQL Apply. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). The problem which could arise out of this situation is that the sane . Suppose there are 3 nodes in the following situation. In the figure, Node 2 is now the active instance connected to the Oracle database and servicing applications and users. Fast Recovery Area manages local recovery-related files. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. The voting result is similar to clusterware voting result. Off-load read-only, reporting, testing and backup activities to the standby database. Voting disk is used by Oracle Cluster Synchronization Services Daemon (ocssd) on each node, to mark its own attendance and also to record the nodes it can communicate with. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. With Oracle Clusterware, . 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. Provides maximum protection from physical corruptions. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. For physical standby databases, this solution: Supports very high primary database throughput. 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. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. Oracle RAC Split Brain Syndrome Scenerio - Oracle Forums Split Brain Syndrome in RAC - I am a DBA The combination of Oracle RAC and Oracle Data Guard provide the most comprehensive architecture for reducing downtime for scheduled outages and preventing, detecting, and recovering from unscheduled outages. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. 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. The servers on which you want to run Oracle Clusterware must be running the same operating system. 3. Communication among the nodes is optimized by means of Redundant Interconnect Usage (without requiring the use of bonding or other technologies) to provide stability, reliability, and scalability. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. The individual nodes are running fine and can accept user connections and work . 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. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. 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 . Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. Maximum RTO for instance or node failure is in minutes. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. 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. Use a physical standby database if read-only access is sufficient. This figure shows Oracle Database with Oracle RAC architecture for a partitioned three-node database. the. 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 . It also gives users complete control over the routing of change records from the primary database to a replica database. Oracle GoldenGate can capture data changes at the primary database or downstream at a replica database, thus enabling users to build hub-and-spoke network configurations that can support hundreds of replica databases. Hello Friends,Welcome you back on exciting topic, today's session is onNode Membership || Voting Disk || Split Brain Syndrome in Oracle RAC - Real Applicatio. These updates are discarded when the snapshot database is reconverted to a physical standby database. Oracle Data Guard provides more comprehensive data protection and its more efficient network usage allows plenty of room to grow without the expense of upgrading its network. 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)). Support for bidirectional replication and updating anything and anywhere. Suppose there are 3 nodes in the following situation. 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. See the high availability solutions and recommendations for Oracle Application Server, Oracle Enterprise Manager, and Oracle Applications on the MAA Web site at: Oracle Database High Availability Best Practices, Oracle Real Application Clusters Administration and Deployment Guide, Oracle Data Guard Concepts and Administration, Oracle Streams Replication Administrator's Guide, Oracle Fusion Middleware High Availability Guide, Oracle Application Server High Availability Guide, Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)", Corruption Prevention, Detection, and Repair, Online Application Maintenance and Upgrades, Description of "Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance", Section 7.1.3, "Oracle Database with Oracle RAC One Node", Description of "Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover)", Description of "Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover)", Description of "Figure 7-4 Oracle Database with Oracle RAC Architecture", Description of "Figure 7-5 Oracle RAC Extended Cluster", http://www.oracle.com/technetwork/database/clustering/overview/, Description of "Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover", Description of "Figure 7-7 Oracle Database with Oracle Data Guard on Primary and Multiple Standby Sites", Description of "Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard", Description of "Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA". A nationally recognized insurance provider in the U.S. maintains two standby databases in the same Oracle Data Guard configuration: one physical standby and one logical standby database. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Now talking about split-brain concept with respect to oracle . Then there are two cohorts: {1, 2} and {3}. The active site is generally called the production site, and the passive site is called the standby site. The processes that were once co-operating prior to the Split-Brain event occurring, independently modify the same logically shared state, thus leading to conflicting views of system state. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Maximum RTO for instance or node failure is zero for the databaseFootref1. You can configure the failed application connections to fail over to the replica. Oracle Clusterware manages the availability of both the user applications and Oracle databases. Unlike a traditional monolithic database server that is expensive and is not flexible to changing capacity and resource demands, Oracle RAC combines the processing power of multiple interconnected computers to provide system redundancy, scalability, and high availability. Oracle Enterprise Management support for Oracle ASM and Oracle ACFS, Grid Plug and Play, Cluster Resource Management, Oracle Clusterware and Oracle RAC Provisioning and patching, Figure 7-4 shows Oracle Database with Oracle RAC architecture. This is called Split Brain. Figure 7-1 shows a basic, single-node Oracle Database that includes an Oracle ASM instance.Foot1 This architecture incorporates several high availability features, including Flashback Database, Online Redefinition, Recovery Manager, and Oracle Secure Backup. In the figure, the configuration is operating in normal mode in which Node 1 is the active instance connected to Oracle Database that is servicing applications and users. 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. It allows you to select the table columns depending on a set of criteria. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. Oracle Clusterware provides a number of benefits over third-party clusterware. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. The fast-start failover has completed and the target standby database is running in the primary database role. 1. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). 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. 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 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. PDF Oracle Clusterware 12c Release 2 Technical Overview Also, you can use the Oracle Clusterware ability to relocate applications and application resources (using the crsctl relocate resource command) as a way to move the workload to another node so that you can perform planned system maintenance on the production server. Oracle RAC Operational Best Practices for the Cloud Created Date: You should determine if both sites are likely to be affected by the same disaster. Footnote1Architectures for which the MO is high might require additional time and expertise to build and maintain, but offer increased flexibility and capabilities required to meet specific business requirements. Oracle Data Guard provides a number of advantages over traditional solutions, including the following: Fast, automatic or automated database failover for data corruptions, lost writes, and database and site failures, Automatic corruption repair automatically replaces a corrupted block on the primary or physical standby by copying a good block from a physical standby or primary database, Most comprehensive protection against data corruptions and lost writes on the primary database, Reduced downtime for storage, Oracle ASM, Oracle RAC, system migrations and some platform migrations, and changes using Data Guard switchover, Reduced downtime with Oracle Data Guard rolling upgrade capabilities, Ability to off-load primary database activitiessuch as backups, queries, or reportingwithout sacrificing the RTO and RPO ability to use the standby database as a read-only resource using the real-time query apply lag capability, Ability to integrate non-database files using Oracle Database File System (DBFS) as part of the full site failover operations, No need for instance restart, storage remastering, or application reconnections after site failures, Transparent and integrated support for application failover. (See Section 7.1.5 for a complete description.). Where two or more instances . 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. Network addresses are failed over to the backup node. 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. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. If all the sub-clusters are of the same size, the sub-cluster having the lowest numbered node 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. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. The key factors include: Recovery time objective (RTO) and recovery point objective (RPO) for unplanned outages and planned maintenance, Total cost of ownership (TCO) and return on investment (ROI). Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). Oracle Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. 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. Also, to prevent a full cluster outage if either site fails, the configuration includes a third voting disk on an inexpensive, low-end standard network file system (NFS) mounted device. Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). 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. Footnote7Recovery time depends on block media recovery and the time it takes to restore a consistent block from the flashback logs or database backups, and to recover the block by applying all the redo from archive logs and online redo logs. For more information, see Oracle Data Guard Concepts and Administration or the Oracle Streams Replication Administrator's Guide. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. 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. Footnote6Recovery time for human errors depend primarily on detection time. A highly available application must analyze every component that affects the application, including the network topology, application server, application flow and design, systems, and the database configuration and architecture. To avoid splitbrain, node 2 aborted itself. Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. The SELECT statement is used to retrieve information from a database. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. split brain syndrome. High Availability Architectures and Solutions - Oracle