The following list summarizes the advantages of using Oracle Data Guard compared to using remote mirroring solutions: Better network efficiencyWith Oracle Data Guard, only the redo data needs to be sent to the remote site and the redo data can be compressed to provide even greater network efficiency. Typically, this is not possible with remote mirroring solutions. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware. Oracle Automatic Storage Management (Oracle ASM) and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and usage. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. which node first joined the cluster). 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. (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. 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. 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 group(cohort) with lower node member survive, in case of same number of node(s) available in each group. pagespeed.lazyLoadImages.overrideAttributeFunctions(); In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Flexible propagation and management of data, transactions, and events. For example, you can put the files on different disks, volumes, file systems, and so on. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. We will verify that when an equal number of database services are running on both nodes, the node with lower node number (host01) survives. It is based on proven Oracle high availability technologies and recommendations. The figure shows users making local updates to the snapshot standby database. Oracle Clusterware provides a number of benefits over third-party clusterware. 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/. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). High availability solution with added data and disaster recovery protection. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). Since I will only explore the scenarios for which functionality has been modified, i.e. 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. Simulate loss of connectivity between two nodes. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. The following list describes some implementations for a multiple standby database architecture: Continuous and transparent disaster or high availability protection if an outage occurs at the primary database or the targeted standby database, Regional reporting or reader databases for better response time, Synchronous redo transport that transmits to a more local standby database, and asynchronous redo transport that transmits to a more remote standby database for optimum levels of performance and data protection, Transient logical standby databases (described in Section 3.6.3) for minimal downtime rolling upgrades, Test and development clones using snapshot standby databases (described in Section 3.6.4), Scaling the configuration by creating additional logical standby databases or snapshot standby databases. Oracle recommends that you create and store the local backups in the fast recovery area. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. From the entry point to an Oracle Application Server system (content cache) to the back-end layer (data sources), all the tiers that are crossed by a request can be configured in a redundant manner with Oracle Application Server. Split Brain Syndrome, In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. 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. Commonly, one will see messages similar to the followings in ocssd.log when split brain happens: Above messages indicate the communication from node 2 to node 1 is not working, hence node 2 only sees 1 node, but node 1 is working fine and it can see two nodes in the cluster. End-users connect to clusters through a public network. 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. Off-load read-only, reporting, testing and backup activities to the standby database. If the node running your Oracle RAC One Node becomes overloaded, you can relocate the instance to another node in the cluster using the online database relocation utility (srvctl relocate database), with no downtime for application users. During the process of resolving conflicts, information may be lost or become corrupted. There are three typical causes of corruption: For high availability, Oracle recommends that you have a minimum of three voting disks. 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. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. 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. Split Brain Syndrome: In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. 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 instance member fails to connect or ping to one . host01 is retained as it has a lower node number. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. split brain syndrome. Furthermore, operational practices across role transitions are simplified when the sites are symmetric. The heartbeat is maintained by background processes like LMON, LMD, LMS and LCK. 2. More investment and expertise to build and maintain an integrated high availability solution is available. In a "split brain" situation, voting disk is used to determine which node (s) will survive and which node (s) will be evicted. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. the number of database services executing on a node. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. 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. 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. Whatever the case, these Oracle RAC interview questions and answers are for you. When a database is started, Oracle Database allocates a memory area called the System Global Area (SGA) and starts one or more Oracle Database processes. Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply. In Oracle RAC, all the instances/servers communicate with each other using a private network. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. 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. Footnote1Applications (or a portion of an application) connected to the system that is being maintained may be temporarily affected. However, remote mirroring solutions affect DBWR process performance because they subject all DBWR process write I/O's to network and disk I/O induced delays inherent to synchronous, zero-data-loss configurations. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. 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. Network addresses are failed over to the backup node. This architecture is referred to as an extended cluster. Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. 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. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. Footnote3The initial investment to build a robust solution is well worth the long-term flexibility and capabilities that Oracle GoldenGate delivers to meet specific business requirements. Providing application-specific failure detection means Oracle Clusterware can fail over not only during the obvious cases such as when the instance is down, but also in the cases when, for example, an application query is not meeting a particular service level. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. The new primary database starts transmitting redo data to the new standby database. For example, if the extended cluster configuration is set up properly, it can protect against disasters such as a local power outage, an airplane crash, or a flooded server room. If you configure a single voting disk, then you should use external mirroring to provide redundancy. 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. Oracle RAC Operational Best Practices for the Cloud Created Date: The common voting result will be: a. See Oracle Data Guard Broker for a detailed description of the observer. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. Different character sets are required between the primary database and its replicas. Footnote8With automatic block repair, this should be the most common block corruption repair. Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. Suppose there are 3 nodes in the following situation. In a typical example, the maximum distance between the systems connected in a point-to-point fashion and running synchronously can be only 10 kilometers. host01 is evicted although it has a lower node number. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. These devices convert ESCON or Fibre Channel to the appropriate IP, ATM, or SONET networks. Building on top of the local high availability solutions is the Oracle Application Server disaster recovery solution. In a non-RAC Oracle database, a single instance accesses a single database. 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 previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. Site configurations are on heterogeneous platforms. They will enhance your knowledge and help you to emerge as the best candidate. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). At the snapshot standby database redo data is received, but it is not applied until the snapshot standby database is reconverted to a physical standby database. Online Patching allows for dynamic database patching of typical diagnostic patches. This is called Split Brain. 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. Clients are connected to the logical standby database and can work with its data. 12) Mention what is split brain syndrome in RAC? 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. Then this process is referred as Split Brain Syndrome. The fast-start failover has completed and the target standby database is running in the primary database role. 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. 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. Let say 2 node RAC configuration node 1 is defined as master node (by some parameter like load and others) incase of network failures node 1 will terminate node 2 . Starting from 12.1.0.2, during split brain resolution, the new algorithm followed to decide the nodes to be evicted/retained is as follows: Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed. 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. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). This unique solution combines the proven Oracle Data Guard technology in Oracle Database with advanced disaster recovery technologies in the application realm to create a comprehensive disaster recovery solution for the entire application system. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. Maximum RTO for instance or node failure is in seconds. sub-clusters are of equal size, I have shut down one of the nodes so that there are only 2 active nodes in the cluster. Note, however, that the synchronous redo transport does not impose any physical distance limitation. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. Zero downtime when using the provisioning capability in Oracle Enterprise Manager Grid Control. . During normal operation, the production site services requests; in the event of a site failover or switchover, the standby site takes over the production role and all requests are routed to that site. The group(cohort) with more cluster nodes survive 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. SELECT statements might be as straightforward as selecting a few . 2. Another possible configuration might be a testing hub consisting of snapshot standby databases. Maximum RTO for instance or node failure is zero for the databaseFootref1. The sum of benefits of Oracle Clusterware with Oracle Data Guard, Best high availability, data protection, and disaster-recovery solution with scalability built in, The sum of benefits of Oracle RAC with Oracle Data Guard, Oracle Database with Oracle GoldenGateFoot3, Bidirectional replication and information management, Replica database (or databases) available for read/write use, Fast failover for computer failure and storage failure, Minimum downtime for computer or site maintenance and database and application upgrades. Oracle RAC One Node provides relocation of Oracle RAC primary and standby databases configured with Oracle Data Guard (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)). 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. What Is Oracle RAC. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle RAC One Node database. With Oracle Clusterware, . Upon detecting the break in communication, the observer attempts to reestablish a connection with the primary database for the amount of time defined by the FastStartFailoverThreshold property before initiating a fast-start failover. Fast-Start Fault Recovery bounds and optimizes instance and database recovery times to minutes. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. Fast Recovery Area manages local recover-related files automatically. Now talking about split-brain concept with respect to oracle RAC systems, it occurs when the instance 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. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. Outages or data loss that could affect customer service and safety are avoided by using Oracle Data Guard synchronous transport and automatic failover (fast-start failover). At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. Oracle Quality of Service (QoS) Management for policy-based run-time management of resource allocation to database workloads to ensure service levels are met in order of business need under dynamic conditions. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. Includes all of the features required for cluster management, including node membership, group services, global resource management, and high availability functions such as managing third-party applications, event management, and Oracle notification services that enable Oracle clients to reconnect to the new primary database after a failure. 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. Check that only two nodes (host01 and host02) are active and host01 has lower node number: Create two singleton services for the RAC database admindb: Verify that admindb is the only database in the cluster having its instances executing on host01 and host02. The problem which could arise out of this situation is that the sane . In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. You can configure the failed application connections to fail over to the replica. Limited support for mixed platforms. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. Better functionalityOracle Data Guard provides full suite of data protection features that provide a much more comprehensive and effective solution optimized for data protection and disaster recovery than remote mirroring solutions. The system resources can be dynamically allocated and deallocated depending on various priorities. Oracle Clusterware manages the availability of both the user applications and Oracle databases. 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. The instances monitor each other by checking "heartbeats." Where two or more instances . Suppose there are 3 nodes in the following situation. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. A global provider of information services to legal and financial institutions uses multiple standby databases in the same Oracle Data Guard configuration to minimize downtime during major database upgrades and platform migrations. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. 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. The voting result is similar to clusterware voting result. Oracle GoldenGate is optimized for replicating data. Oracle RAC One Node allows you to run one instance of an Oracle RAC database on a single node in a cluster. b. Online Patching allows for dynamic database patches for diagnostic and interim patches. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). Support for heterogeneous platforms, versions, and character sets. 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. 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. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. Oracle Enterprise Manager support for patch application simplifies software maintenance. 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. 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. The Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. 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. Applications can easily mask failures to the end user. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. the number of database services executing on a node. For more information, see Oracle Data Guard Concepts and Administration or the Oracle Streams Replication Administrator's Guide. Fast Recovery Area manages local recovery-related files. Thus, this feature allows you to consolidate many databases into a single cluster for easier management, while still providing high availability by quickly relocating instances in the event of server failure. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. Database scalability beyond one instance or node. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. With Database Server Grid and Database Storage Grid (described in Section 5.2 and Section 5.3), you can build standby database and testing hubs that use a pool of system resources.