In previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. These devices convert ESCON or Fibre Channel to the appropriate IP, ATM, or SONET networks. The servers on which you want to run Oracle Clusterware must be running the same operating system. Split Brain Resolution in Oracle Clusterware 12c Rel 2 1. 1. Maximum RTO for instance or node failure is in minutes. 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. 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. What is split brain in Oracle RAC? Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. Fast Recovery Area manages local recover-related files automatically. 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. Q39) Mention what is split brain syndrome in RAC? 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. Each site is a self-contained system. End-users connect to clusters through a public network. Applications can easily mask failures to the end user. Why is it like that? These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. 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. 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. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. 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. The fast-start failover has completed and the target standby database is running in the primary database role. 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. Oracle Automatic Storage Management and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and utilization. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. 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. The center frame shows the configuration during fast-start failover. 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. 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. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. The logical standby database may contain additional indexes and materialized views. 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. In Oracle RAC each node in the cluster is interconnected through a private interconnect. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. Logical or user failures that manipulate logical data (DMLs and DDLs). 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)). Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. We will verify that when an unequal number of database services are running on the two nodes, the node hosting the higher number of database services survives even if it has a higher node number. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. split brain syndrome. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. 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. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. Name of the cluster: Cluster01.example.com, Number of nodes: 3 (host01, host02, host03), Instances of RAC database: admindb1 on host01. 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. There are some corruptions that cannot be addressed by automatic block repair, and for those we can rely on Data Guard failover that takes seconds to minutes. It allows you to select the table columns depending on a set of criteria. Oracle Restart enhances the availability of Oracle databases, listeners, and Oracle ASM instances in a single-instance environment by monitoring and automatically restarting Oracle processes. 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. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. (adsbygoogle=window.adsbygoogle||[]).push({}); The biggest risk following a Split-Brain event is the potential for corrupting system state. Support for bidirectional replication and updating anything and anywhere. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Unlike the cold cluster model where one node is completely idle, all instances and nodes can be active to scale your application. For more information, see the "Administering Oracle RAC One Node" section in the Oracle Real Application Clusters Administration and Deployment Guide. This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. Suppose there are 3 nodes in the following situation. See Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)" for more information about the best practices documentation. For virtualization, Oracle RAC One Node with Oracle VM increases the benefit of Oracle VM with the high availability and scalability of Oracle RAC. The heartbeat is maintained by background processes like LMON, LMD, LMS and LCK. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. 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. An Oracle RAC extended cluster is an architecture that provides extremely fast recovery from a site failure and allows for all nodes, at all sites, to actively process transactions as part of single database cluster. 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. It also allows the storage to be laid out in a different fashion from the primary computer. During the process of resolving conflicts, information may be lost or become corrupted. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. which node first joined the cluster). 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. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. As the result, 1 or more instance(s) will be evicted. Fine control of information and data sharing are required. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. The group(cohort) with more cluster nodes survive All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. 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. Site configurations are on heterogeneous platforms. Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. These solutions are categorized into local high availability solutions that provide high availability in a single data center deployment, and disaster-recovery solutions, which are usually geographically distributed deployments that protect your applications from disasters such as floods or regional network outages. 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. 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. 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. 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. 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. You can have up to 32 voting disks in your cluster. 817202 Mar 1 2016 edited Mar 2 2016. For logical standby databases, this solution: Provides the simplest form of one-way logical replication, Allows for structural changes to the standby database, such as changes to local tables, adding schemas, indexes, and materialized views, Off-loads production by providing read-only access to a synchronized standby database and allows read/write access to local tables that are not being modified by the primary database, All of the business benefits of Oracle Clusterware (cold cluster failover) and Oracle Data Guard. SELECT statements might be as straightforward as selecting a few . The configuration can be an active-active configuration using Oracle Application Server Cluster or an active-passive configuration using Oracle Application Server 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. The production database is connected over the network to the physical standby database site and the logical standby database site (the standby databases may be at the same or different sites). They will enhance your knowledge and help you to emerge as the best candidate. 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. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. 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. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. 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. 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 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). 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. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. Flexible propagation and management of data, transactions, and events. End-users connect to clusters through a public network. Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply.
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