How to determine the CRSVersion?Filed under:Clusterware Tags:Clusterware syedracdba @ 4:33 pmThe active version or the software version of Cluster (CRS) can be verified with following commands. These versions details are required while upgrading a cluster.To check the Active VersionRun the following command on the local node.$ crsctl query crs activeversionCRS active version on the cluster is [10.2.0.3.0]Note:The active version is the lowest software version running in a cluster.To check the Software VersionRun the following command on the local node.$ crsctl query crs softwareversionCRS software version on node [racnod01] is [10.2.0.3.0]Note:The software version is the binary version of the software on a particular cluster node.What is Oracle RAC One Node?

Oracle introduced a new option called RAC One Node with the release of 11gR2 in late 2009. This option is available withEnterpriseeditiononly. Basically, it provides a coldfailoversolution for Oracle databases. Its a single instance ofOracle RACrunning on one node of the cluster while the 2nd node is in a cold standby mode. If the instance fails for some reason, then RAC One Node detects it and first tries to restart the instance on the same node.The instance is relocated to the 2nd node in case there is a failure or fault in 1st node and the instance cannot be restarted on the same node. The benefit of this feature is that it automates the instance relocation without any downtime and does not need a manual intervention. It uses a technology called Omotion, which facilitates the instance migration/relocation. RAC one is Oracles answer or solution to OS clustering solution likeVeritas Storage Foundation,Sun Solaris cluster,IBM HACMP, and HP Service guard etc.

Purpose

Its Oracles attempt to tie customers to a single vendor by eliminating the need to buy 3rd party OS cluster solutions. First, it introducedOracle Clusterwarewith 10g and stopped the need to rely on 3rd party cluster software and now it intends to conquer the rest who are still usingHACMP,Sun Solaris clusteretc. for cold failover.

Benefits

The Oracle RAC One node provides the following benefits:

Built-in cluster failover for high availability Rolling patches for single instance database Proactive migration / failover of the instance Live migration of instances across servers Online upgrade to RAC

The rolling upgrade is really useful. Upgrade to the OS, and Database can be done without any downtime unless upgrade requires some scripts to be run against the database. With RAC One Node, the DBAs and Sys admins can be proactive and migrate/failover the instance to another node to perform any critical maintenance activity.

What it's not suited for

According to me the RAC one node is not a viable or recommended solution in the following scenarios:

To load balance unlike regular RAC A true high availability solution As a DR solution; Data guard best suits the bill For mission critical applications

Cost

It is definitely not FREE. Oracle has priced RAC one at par withActive Data Guard. The RAC One node is priced separately and costs $10,000 per processor as against $23,000 for regular RAC. The licensing cost is required for ONE node only (in a 2-node setup). RAC one node is eligible for 10-day rule, allowing a customer to migrate to another without the need to buy additional license up to 10-days in a calendar year. People arguing against paying a license fee for resources they are not using will still lament.

Conclusion

I am still not very convinced on the usefulness of RAC one node. I think customers invest in RAC for their mission critical applications and achieving high availability and load balancing at the same time. Those who dont go for RAC rely on Data Guard and now with 11g, on Active Data Guard. So dont see a huge requirement for RAC One except seamless failover within a data center. The licensing is a bit disappointing; they are making clients pay $10 K. Moreover RAC is free withStandard editionthough one doesnt getenterprise featuresand limited to 4 CPU sockets only. So, thinking RAC One will be popular among customers who are currently using standard edition and want to switch to enterprise will be wrong. However, this is still a very new feature and as more people adopt it, we will get more clarity on its usability. I am planning to do a POC on it and would publish the installation steps and any findings (goods things and not so good things) of my POC.

A cluster comprises of multiple interconnected servers or computers that appear as if they are one single server to end users and applications.What is RAC ?RAC stands for Real Application Clusters. It allows multiple nodes in a clustered system to mount and open a single database that resides on shared disk storage. Should a single system fail (node), the database service will still be available on the remaining nodes.In RAC database, comprises of multiple instances, however there will be only one database.A non-RAC database is only available on a single system. If that system fails, the database service will be down (single point of failure).Oracle Database 10g Real Application Clusters (RAC) enables the clustering of the Oracle Database. A RAC database comprises of multiple instances residing on different computers to access a common database residing on shared storage.Why Real Application Cluster ?The basic principle behind the Real Application Cluster is greater throughput and scalability due to the combined power of multiple instances running on multiple serversReal Application Cluster provides high availability and scalability for all application types. The RAC infrastructure is also a key component for implementing the Oracle enterprise grid computing architecture. Multiple instances access a single physical database prevents the server from being a single point of failure. Combining smaller servers into a cluster can be achieved to create scalable environment that support mission critical business applications.Real application Cluster uses Oracle Cluster ware for the infrastructure to bind multiple servers so that they operate as a single system.Oracle Clusterware is a portable cluster management solution that is integrated with the Oracle database. The Oracle Clusterware is also a required component for using Real application Cluster.In Oracle Database 10g, Oracle Provides you with an integrated software solution that addresses cluster management, event management, application management, connection management, storage management, load balancing and availability. These capabilities are addressed while hiding the complexity through simple-to-use management tools and automation.Oracle Real Application Clusters 10g provides an integrated cluster ware layer that delivers a complete environment for applications.Oracle Real Application Cluster (RAC) uses Oracle Clusterware for the infrastructure to bind multiple servers so that they operate as a single systemMain Components of Oracle Real Application Cluster 10gIt comprises of two main components1. Oracle Clusterware2. Oracle SoftwareIn RAC 10g Clusterware is called CRS layer which resides below Oracle software Layer. Second layer is the Oracle software itself.Oracle Real Application Cluster (RAC) is the Oracle Database option that provides a single system image for multiple servers to access one Oracle database. In RAC, each Oracle instance usually runs on a separate server.Oracle Clusterware is software, enables the servers to be bound together to operate as if they were one server. The Oracle Clusterware comprises of two clusterware components: a voting disk to record node membership information and the Oracle Cluster Registry (OCR) to record cluster configuration information. In Oracle Clusterware each node is connected to a private network by way of a private interconnect.The Oracle Clusterware comprises several background processes that facilitate cluster operations such as Cluster Synchronization Service (CSS) and Event Management (EVM).What are the Real Application Cluster Main Processes ?The main processes involved in Oracle RAC are primarily used to maintain database coherency among each instance. They manage what is called the global resources. LMON: Global Enqueue Service Monitor LMD0: Global Enqueue Service Daemon LMSx: Global Cache Service Processes. Where x can range from 0 to j LCK0: Lock Process DIAG : Diagnostibility ProcessThere are several tools that are used to manage the various resources available on the cluster at a global level. Some of the tools used are Server Control (SRVCTL), DBCA and Enterprise Manager.Oracle Clusterware is a portable cluster management solution that is integrated with the Oracle database. The Oracle Clusterware enables you to create a clustered pool of storage to be used by any combination of single-instance and RAC databases.Oracle Clusterware is the only clusterware that you need for most platforms on which RAC operates. You can also use clusterware from other vendors if the clusterware is certified for RAC.The combined processing power of the multiple servers can provide greater throughput and scalability than is available from a single server. RAC is the Oracle Database option that provides a single system image for multiple servers to access one Oracle database. In RAC, each Oracle instance runs on a separate server.RAC is a unique technology that provides high availability and scalability for all application types. The RAC infrastructure is also a key component for implementing the Oracle enterprise grid computing architecture. Having multiple instances access a single database prevents the server from being a single point of failure. RAC enables you to combine smaller commodity servers into a cluster to create scalable environments that support mission critical business applicationsWhat are the Storage Principles for RAC Software and CRS ?The Oracle Software 10g Real Application Clusters installation is a two-phase installation in the first Phase, You install CRS. In the second phase, you install the Oracle Database software with RAC components and create a cluster database.The oracle home that you use for the CRS software must be different from the one that is used for the RAC Software. CRS and RAC software is installed on cluster shared storage.Note:-Cluster Software and Oracle software is usually installed on a regular file system that is local to each node. This permits online patch upgrades without shutting down the database and also eliminates the software as a single point of failure.Do you need special hardware to run RAC ?RAC requires the following hardware components: A dedicated network interconnect - might be as simple as a fast network connection between nodes; and a shared disk subsystem.RAC and Shared Storage Technologies1. Supported shared storage for Oracle grids: Network attached Storage Storage Area Network2. Supported file systems for Oracle grids:- Raw Volumes Cluster file system ASM

Oracle Real Application Cluster & High AvailabilityOracle Real Application Cluster (RAC) is a cluster database. Compared to traditional shared-nothing architecture of single instance database, oracle Real Application Cluster has shared cache architecture and also shared-disk approaches to provide highly available and scalable solution for any business applications.One of the key components of Oracle enterprise grid architecture by oracle is the Real application Cluster (RAC)Oracle RAC is a unique technology that provides high availability and scalability for all application types. The Oracle RAC infrastructure is also a key component for implementing the Oracle enterprise grid computing architecture. Having multiple instances access a single database prevents the server from being a single point of failure. Oracle RAC enables you to combine smaller commodity servers into a cluster to create scalable environments that support mission critical business applications. Applications that you deploy on Oracle RAC databases can operate without code changes.Unique feature called Fast Application Notification (FAN) configuration in oracle Real application cluster helps load balancing when available service status change. Available service status can change during a scheduled outage for patching or any other regular maintenance task. Service status can also change due to unexpected faults such as node reboot, database service unavailability etc.Oracle Real Application Cluster has some cost effective options while scaling up or scaling down your size of application usage volume. Olden days normally businesses have to pre-plan the scale of their application few years in advance. Though they did not made use of the full capacity at the initial stage of deployment, the hardware had to be in place in anticipation of high growth in the future. This kind of planning did add additional cost to Businesses in planning their hardware and also software licensing. In case of miscalculation of capacity, did cost further cost in moving their application to higher capacity servers in later stages. Once the application is deployed and up and running and if you decide to migrate to different server, it does cost additional overhead in terms of building servers, outages, manpower etc etc. So migrating the application is not an easy exercise and if your business is cost conscious (All business are cost conscious I guess) this type of migration related to scaling up or scaling down should be avoided.So what is the cost effective solution to avoid these overheads? That is where Oracle Real application Cluster comes to your rescue.Why Oracle Real application Cluster?To accommodate unplanned, unanticipated growth in any business application, oracle real application cluster can be built from standard, commodity-priced processors, with standard network and storage components. Since oracle Real application Cluster is built on very foundation of Grid computing, when you require more processing power or wish to scale up, simply add another similar commodity priced server. Adding new server doesnt require you to bring down the database and this can be done without interrupting the service with users still accessing the database. Oracle Real application cluster supports up to 100 nodes in any given Cluster configuration.If your business decides that you need to scale down your application for whatever reason, you could de-commission some of the servers, without bringing down your database and while users still accessing the database without any interruption.What is a Cluster?A cluster comprises of multiple interconnected servers or computers that appear as if they are one single server to end users and applications.Oracle Database 10g Real Application Clusters (RAC) enables the clustering of the Oracle Database. A RAC database comprises of multiple instances residing on different computers to access a common database residing on shared storage.The basic principle behind the Real Application Cluster is greater throughput and scalability due to the combined power of multiple instances running on multiple serversSome of the main benefits of Oracle Real Application Cluster (RAC) Scalability:Service capacity can be expanded simply by adding servers to existing cluster. Availability round the clock (24/7):Zero downtime for database applications. Relatively lower computing cost:Cost can be relatively reduced by using low-cost commodity hardware. Grid Computing:Very foundation of Oracle Grid computing is oracle Real Application Cluster (RAC.Main Components of Oracle Real Application Cluster 10g.It comprises of two main components1. Oracle Clusterware2. Oracle SoftwareIn RAC10g Clusterware is called CRS layer which resides below Oracle software layer. Second layer is the Oracle software itselfRAC is the Oracle Database option that provides a single system image for multiple servers to access one Oracle database. In oracle Real application cluster, each Oracle instance usually runs on a separate server.However when it comes to managing and looking after your production Real application Cluster, it may not be practical to find the commands you needed in the right time and possibly you dont want to keep searching for the right command and tips when you have a major production issue and the users cannot access the database.This book "Oracle Real Application Cluster Field DBA Admin Handbook" describes how to administer the Oracle Clusterware and Oracle Real Application Clusters (Oracle RAC) architecture and provides an overview of these products. Describes services and storage and how to use RAC scalability features to add and delete instances and nodes in RAC environments.This book "Oracle Real Application Cluster Field DBA Admin Handbook" also describes, how to use the Server Control (SRVCTL) utility to start and stop the database and instances, manage configuration information, and to delete/add or move instances and servicesTroubleshooting section describes how to interpret the content of various RAC-specific log files, search on Metalink and also useful reference section with relevant Metalink Document reference and WeblinksStorage in Oracle Real Application ClustersStorage for Real application cluster databases must be shared. In other words, datafiles must reside on cluster file system, shared raw devices or Automatic Storage Management (ASM) disk group.The shared storage must include datafiles, undo tablespaces for each instance and also online redo log files. It is highly recommended by oracle to use server parameter file spfile (SPFILE) instead of parameter file (PFILE).Shared storage Technologies and RAC1. Supported shared storage for Oracle grids Network attached Storage Storage area Network2. Supported file systems for Oracle grids Raw Volumes Cluster file system ASMStorage Area Network (SAN) represents the evolution of data storage technology. Traditionally, on client server systems, data was stored on devices either inside or directly attached to the server. Next in the evolution scale came Network Attached Storage (NAS) that took the storage devices away from the server and connected them directly to the network.In RAC deployment, choosing the appropriate file system is critical. Because traditional file systems do not support simultaneous mounting by more than one system, you must store files in either raw volumes without any file system, or on a file system that supports concurrent access by multiple systems.Oracle Cluster File systemsOracle cluster file system (OCFS) is a shared file system designed specially for oracle Real Application ClusterAutomatic Storage Management (ASM) Automatic and high-performance cluster file system Manages Oracle Database files Data spread across disks to balance load Integrated mirroring across disks Solves many storage management ChallengesThe automatic storage management(ASM) is a new feature in oracle Database 10g. It provides a vertical integration of the file system and the volume manager that is specially built for Oracle Database filesThe ASM distributes I/O load across all available resources to optimize performance while removing the need for manual I/O tuning. ASM facilitates management of dynamic database environment by allowing DBAs to increase the database size without having to shut down the database to adjust the storage allocations.The ASM can maintain redundant copies of data to provide fault tolerance.Note:-ASM is the oracles strategic and stated direction as to where oracle database files should be stored. However OCFS will continue to be developed and supported for those who are using it.Comparison between RAW or CFS Using CFS1. Simple management2. Use of OMF with RAC3. Single Oracle Software installation4. Autoextend Using raw1. Performance2. Use when CFS not available3. Cannot be used for archive log filesYou can use a cluster file system or place files on raw devices.Cluster file systems provide the following advantages:- Greatly simplify the installation and administration of RAC Use of Oracle Managed Files with RAC Single Oracle Software installation Autoextend enabled on oracle data files Uniform accessibility to archive logs in case of physical node failureRAW devices Implications Raw devices are always used when CFS is not available or not supported by oracle Raw devices offer best performance without any intermediate layer between oracle and the diskWhat is Automatic Storage ManagementAutomatic storage management (ASM) is a new feature in Oracle Database 10g from oracle . It integrates file system and the Logical Volume Manager (LVM) . In ASM Volume Manager is specifically built for Oracle database files. The ASM can provide management for single SMP machines or across multiple nodes of a cluster for Oracle Real Application Clusters support.Automatic Storage Management (ASM) simplifies administration of Oracle related files by allowing the administrator to reference disk groups rather than individual disks and files, which are managed by ASM.Manual I/O tuning can be eliminated while ASM distributes input/output (I/O) load across all available resources to optimize performance while removing the need for manual I/O tuning.The ASM has the flexibility of maintaining redundant copies of data to provide fault tolerance, or it can be built on top of vendor-supplied reliable storage mechanisms. Data management in ASM is basically done by choosing the desired reliability and performance characteristics for classes of data rather than with human interaction of per-file basis.Automated storage management gives the time to DBAs by increasing their ability to manage larger databases and more of them with increased efficiency.Automatic Storage Management (ASM) is a feature in Oracle Database 10g/11g that provides the database administrator with a simple storage management interface that is consistent across all server and storage platforms. ASM provides the performance of async I/O with the easy management of a file system.Some of the Key features of ASM Stripes files rather than logical volumes Enables online disk reconfiguration and dynamic rebalancing Provides adjustable rebalancing speed Provides file based redundancy Supports only Oracle files Its cluster awareWhy ASM ?Some of the storage management features with ASM include Striping Mirroring Asynchronous I/O Direct I/O SAME and Load Balancing Is automatically installed as part of the base code setASM includes striping and mirroring to provide balanced and secure storage. The level of redundancy and the granularity of the striping can be controlled using templates. The new ASM functionality can be used in combination with existing raw and cooked file systems, along with OMF and manually managed files.Direct I/OBy making use of Direct I/O, higher cache hit ratio can be achieved. Buffered I/O uses most important resources like CPU and memory. In case of buffered I/O Oracle blocks are cached both in the SGA and in the file system buffer cache.Buffered I/O fills up the file system cache with Oracle Data, where as using the Direct I/O allows non-Oracle data to be cached in the file system much more efficiently.Key Features and Benefits of ASMThe ASM functionality is controlled by an ASM instance.The main components of ASM are disk groups, each of which comprise of several physical disks that are controlled as a single unit. The physical disks are known as ASM disks, while the files that reside on the disks are know as ASM files.The ASM divides a file into pieces and spreads them evenly across all the disks. The ASM uses an index technique to track the placement of each piece. Traditional striping techniques use mathematical functions to stripe complete logical volumes. The ASM includes mirroring protection without the need to purchase a third-party Logical Volume Manager. One unique advantage of ASM is that mirroring is applied on file basis, rather than on a volume basis. Therefore, the same disk group can contain a combination of files protected by mirroring, or not protected at all.The ASM supports data files, log files, control files, archive logs, Recovery Manager (RMAN) backup sets, and other Oracle database file types. The ASM supports Real Application Clusters (RAC) and eliminates the need for a cluster Logical Volume Manager or a cluster file system.Note:-ASM is shipped with the database and available as part of base code set and there is no need to go through a separate installation in the custom tree installation. It is available in both the Enterprise Edition and Standard Edition installations.One of the flexible feature of ASM is it does not eliminate any existing database functionality which uses non ASM files. Existing database are able to operate as they always have been. New files may be created as ASM files, while existing ones are administered in the old way or can be migrated to ASM.In ASM, at the top of the new hierarchy, you can find what are called ASM disk groups. Any single ASM file is contained in only one disk group. However, a disk group may contain files belonging to several databases, and a single database may use storage from multiple disk groups.ASM files are always spread across all ASM disks in the disk group.The ASM disks are partitioned in allocation units (AU) of on megabyte each. An AU is the smallest contiguous disk space that ASM allocates. The ASM does not allow physical blocks to split across AUs.ASM General ArchitectureTo use ASM, you must start a special instance called an ASM instance before you start your database instance.ASM instances manage the metadata needed to make ASM files available to ordinary database instances. Both ASM instances and database instances have access to a common set of disks call disk group. Database instances access contents of ASM files directly, communicating with an ASM instance only to get information about the layout of these files.An ASM instance is like any other database instance except it contains two new background processes. First one coordinates rebalance activity for disk groups and it is called RBAL. The second one performs the actual rebalance activity for AU movements. At any given time there can be many of these, and they are called ARB0, ARB1, and so on. An ASM instance also has most of the same background processes as a ordinary database instance (SMON, PMON, LGWR, and so on.)Each database instance using ASM has two new background processes called ASMB and RBAL. RABL performs global opens of the disks in the disk groups. At database instance startup, ASMB connects as a foreground process into the ASM instance. All communication between the database and ASM instances is performed via this bridge. This includes physical file changes such as data file creation and deletion. Over this connection, periodic messages are exchanged to update statistics and to verify that both instances are healthyIt is quite possible to cluster ASM instances and run them as RAC, using the existing Global Cache Services (GCS) infrastructure. There is one ASM instance per node on a cluster.Storage in Oracle Real Application ClustersStorage for RAC databases must be shared. In other words, datafiles must reside in an Automatic Storage Management (ASM) disk group, on a cluster file system, or on shared raw devices. This must include space for an undo tablespace for each instance if you are using automatic undo management. Additionally, for each instance you must create at least two redo log files that reside on shared storage. Oracle recommends, you can use one shared server parameter file (SPFILE) with instance-specific entries. Or you can use a local file system to store client-side parameter files (PFILEs).If you do not use ASM, if your platform does not support a cluster file system, or if you do not want to use a cluster file system to store datafiles, then create additional raw devices as described in your platform-specific Oracle Real Application Clusters installation and configuration guide.Automatic Storage Management in Real Application ClustersASM automatically optimizes storage to maximize performance by managing the storage configuration across the disks. ASM does this by evenly distributing the storage load across all of the available storage within your cluster database environment. ASM partitions your total disk space requirements into uniformly sized units across all disks in a disk group. ASM can also automatically mirror data to prevent data loss. Due to these added features, ASM significantly reduces administrative overhead.As in single-instance Oracle databases, To use ASM in RAC, select ASM as your storage option when you create your database with the Database Configuration Assistant (DBCA).Note:-using ASM in RAC does not require I/O tuning.Automatic Storage Management Components in RACWhen you create your database, Oracle creates one ASM instance on each node in your RAC environment if one does not already exist. Each ASM instance has either an SPFILE or PFILE type parameter file.The shared disk requirement is the only substantial difference between using ASM in a RAC database compared to using it in a single-instance Oracle database. ASM automatically re-balances the storage load after you add or delete a disk or disk group.In a cluster, each ASM instance manages its node's metadata updates to the disk groups. In addition, each ASM instance coordinates disk group metadata with other nodes in the cluster. As in single-instance Oracle databases, you can use Enterprise Manager, DBCA, SQL*Plus, and the Server Control Utility (SRVCTL) to administer disk groups for ASM in RACAutomatic Storage ManagementASM automatically optimizes storage to maximize performance by rebalancing the storage configuration across the disks that ASM manages. ASM spreads the storage load across all available storage within your cluster database environment for optimal performance. ASM partitions your total disk space into uniformly sized units across all disks in a disk group.ASM functionality is controlled by an ASM instance.The main components of ASM are disk groups, each of which comprise of several physical disks that are controlled as a single unit. The physical disks are known as ASM disks, while the files that reside on the disks are know as ASM files.What is a raw device ?A raw device is a disk drive that does not yet have a file system set up. Raw devices are used for Real Application Clusters since they enable the sharing of disks.The term raw devices applies to the character oriented disk device files (as opposed to the block oriented ones) normally found in /dev. These device files are a part of the interface between the hardware disks and the UNIX system software.Raw devices are character devices. A utility called raw can be used to bind a raw device to an existing block device. These "existing block devices" may be disks or cdroms/dvds.Raw Partition:A raw partition is a portion of a physical disk that is accessed at the lowest possible level. A raw partition is created when an extended partition is created and logical partitions are assigned to it without any formatting. Once formatting is complete, it is called cooked partitionSCSI, SAN and NAS, iSCSIAlthough not directly related to CFS and raw devices questions arise around the storage technologies being used.SCSI:Disk drives are connected individually to the host machine by small computer system interfaces (SCSI) through one of a number of disk controllers.SAN:Storage Area Network is a shared dedicated high-speed network connecting storage elements and the backend of the servers.NAS:Network Attached Storage is a special purpose server with its own embedded software that offers cross platform file sharing across the network.iSCSI:Another form of network attached storage that communicates in block mode over Ethernet (Gigabit Ethernet) to special storage subsystems. Like NFS attached storage, iSCSI uses standard hardware and software to communicate - although a private network is recommended. Because it operates in block mode, use of iSCSI with RAC requires either a cluster file system or use of raw volumes.Raw devices suitable for complex applications like Database Management Systems that typically do their own caching because, raw device offers a more "direct" route to the physical device and allows an application more control over the timing of IO to that physical device. A raw device can be bound to an existing block device (for example a disk) and be used to perform "raw" IO with that existing block device. Such "raw" IO bypasses the caching that is normally associated with block devicesIn most UNIX systems it is a performance advantage to use raw device files for data storage. By using raw devices, the UNIX file system is bypassed and the operating system is able to perform more effective I/O.Since file size is fixed by the size of the partition, because of this, file size is constrained by the size of the partition. If the partition becomes full, the raw device file must be moved to a larger partition. In the worst case, the disk must be reformatted in order to create a larger partition.What is a Cluster File system (CFS) ?A cluster file system (CFS) is a file system that may be accessed (read and write) by all members in a cluster at the same time. This implies that all members of a cluster have the same view.If your platform supports an Oracle certified cluster file system, you can store the files that Real Application Clusters requires directly on the cluster file system.Aclustered file systemis a file system which is simultaneously mounted on multiple servers. There are several approaches to clustering, most of which do not employ a clustered file system. While many computer clusters don't use clustered file systems, unless servers are underpinned by a clustered file system the complexity of the underlying storage environment increases as servers are added.Distributed file system- the generic term for a client/server or "network" file system where the data isn't locally attached to a host.Global file system- this refers to the namespace, so that all files have the same name and path name when viewed from all hosts. This obviously makes it easy to share data across machines and users in different parts of the organization.OCFS2 (Oracle Cluster File System 2) is a free, open source, general-purpose, extent-based clustered file system which Oracle developed and contributed to the Linux community, and accepted into Linux kernel 2.6.16.OCFS2 provides an open source, enterprise-class alternative to proprietary cluster file systems, and provides both high performance and high availability. OCFS2 provides local file system semantics and it can be used with any application. Cluster-aware applications can leverage parallel I/O for higher performance, and other applications can make use of the file system to provide a fail-over setup to increase availability.Cluster file system- a distributed file system that is not a single server with a set of clients, but instead a cluster of servers that all work together to provide high performance service to their clients. To the clients the cluster is transparent - it is just "the file system", but the file system software deals with distributing requests to elements of the storage cluster.Shared-disk cluster file systemThe most common type of clustered file system is the shared disk file system, in which two or more servers are connected to a single shared storage subsystem, such as a stand-alone RAID array or SAN.Symmetric file system- A symmetric file system is one in which the clients also run the metadata manager code; that is, all nodes understand the disk structures.Asymmetric file system- An asymmetric file system is one in which there are one or more dedicated metadata managers that maintain the file system and its associated disk structures.Shared-nothing clustered file systemAnother clustered file system approach is to have each node use its own local storage, and communicate data changes to other nodes via some network or bus. In this case disks are not shared amongst nodes, but are instead dedicated to a single node and made readable and writable to other serversParallel file system- file systems with support for parallel applications, all nodes may be accessing the same files at the same time, concurrently reading and writing. Data for a single file is striped across multiple storage nodes to provide scalable performance to individual files.SAN file system- These provide a way for hosts to share Fibre Channel storage, which is traditionally carved into private chunks bound to different hosts. To provide sharing, a block-level metadata manager controls access to different SAN devices. A SAN File system mounts storage natively in only one node, but connects all nodes to that storage and distributes block addresses to other nodes. Scalability is often an issue because blocks are a low-level way to share data placing a big burden on the metadata managers and requiring large network transactions in order to access data.Oracle ClusterwareOracle Clusterware is a portable cluster management solution that is integrated with Oracle Database. Oracle Real Application Clusters (Oracle RAC) uses Oracle clusterware as the infrastructure that binds together multiple nodes which operate as a single server. Oracle Clusterware includes a high availability framework for managing any application that runs on your cluster. Voting disk and the OCR is created on shared storage during Oracle Clusterware installation process.The Oracle Clusterware includes two important components: the voting disk and the Oracle Cluster Registry (OCR). The voting disk is a file that manages information about node membership and the OCR is a file that manages cluster and Oracle Real Application Clusters (Oracle RAC) database configuration information.1. Voting Disk: -Manages cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. RAC uses the voting disk to determine which instances are members of a cluster. The voting disk must reside on shared disk. For high availability, Oracle recommends that you have multiple voting disks. The Oracle Clusterware enables multiple voting disks.Note:-If you define a single voting disk, then you should use external mirroring to provide redundancy.2. OCR File :-Cluster configuration information is maintained in Oracle Cluster Registry file. OCR relies on a distributed shared-cache architecture for optimizing queries against the cluster repository. Each node in the cluster maintains an in-memory copy of OCR, along with an OCR process that accesses its OCR cache.When OCR client application needs to update the OCR, they communicate through their local OCR process to the OCR process that is performing input/output (I/O) for writing to the repository on disk.The OCR client applications are Oracle Universal Installer (OUI), SRVCTL, Enterprise Manger (EM), Database Configuration Assistant (DBCA), Database Upgrade Assistant(DBUA), NetCA and Virtual Internet Protocol Configuration assistant (VIPCA). OCR also maintains dependency and status information for application resources defined within CRS, specifically databases, instances, services and node applications.Note:-The name of the configuration file is ocr.loc and the configuration file variable is ocrconfig.locOracle Cluster Registry (OCR) :-Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR also manages information about processes that Oracle Clusterware controls. The OCR stores configuration information in a series of key-value pairs within a directory tree structure. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster. The Oracle Clusterware can multiplex the OCR and Oracle recommends that you use this feature to ensure cluster high availability.Note:-You can replace a failed OCR online, and you can update the OCR through supported APIs such as Enterprise Manager, the Server Control Utility (SRVCTL), or the Database Configuration Assistant (DBCAsrvctl

srvctl is the oracle recommended tool for DBAs to use to interact with CRS and the cluster registry. There are number of tools which can be used to interface with the cluster registry and CRS, however they are undocumented and intended only for use by Oracle Support. srvctl is well documented tool and its also easy to use.srvctl must be run from the $ORACLE_HOME of the RAC you are administering.The basic format of a srvctl command issrvctl[options]where command is one ofenable|disable|start|stop|relocate|status|add|remove|modify|getenv|setenv|unsetenv|configand the target, or object, can be a database, instance, service, ASM instance, or the nodeapps.options extends the use of preceding command, target combinations.To see the online command syntax and options for each SRVCTL command, enter:srvctl verb noun -hSRVCTL for Administering Oracle Real Application ClustersThe Server Control (SRVCTL) utility is installed on each node by default. You can use SRVCTL to start and stop the database and instances, manage configuration information, and to move or remove instances and services. You can also use SRVCTL to add services. SRVCTL also manages configuration information.Some SRVCTL operations store configuration information in the Oracle Cluster Registry (OCR). SRVCTL performs other operations, such as starting and stopping instances, by sending requests to the Oracle Clusterware process (CRSD), which then starts or stops the Oracle Clusterware resources.Some of the the srvctl commands are summarized in this table:Srvctl CommandsCommand Descriptionsrvctl add :-Adds database, instance, service and nodeappssrvctl remove:-Removes database, instance, service and nodeappssrvctl modify :-Modifies database, instance, service and nodeappssrvctl disable:-Disables database, database instance, asm instance and servicesrvctl enable:-Enables database, database instance, asm instance and servicesrvctl start :-Starts database, database instance, asm instance, service and nodeappssrvctl stop :-Stops database, database instance, asm instance, service and nodeappssrvctl status:-Display status of database, database instance, asm instance, service and nodeappsAs you can see, srvctl is a powerful utility. srvctl -help displays a basic usage message, and srvctl -h displays full usage information for every possible srvctl command.To see help for all SRVCTL commands, enter following command from the command line:srvctl hTo see command syntax and list of options fir each SRVCTL commandsrvctl command object -hTo see SRVCTL version numbersrvctl -VFor example:To add named instances to a database:> srvctl add instance -d racdb -i racinst1 -n mynode1 > srvctl add instance -d racdb -i racinst2 -n mynode2 > srvctl add instance -d racdb -i racinst3 -n mynode3For example, to display configured databases:->srvctl config database -d RACDBwhere RACDB is the name of the databaseTo stop database and all or named instances. The syntax is:> srvctl stop database -d database_name [-o stop_options] [-c connect_string]> srvctl stop instance -d database_name -i instance_name [,instance_name_list] [-o stop_options][-c connect_string]To stop the database all instances:> srvctl stop database -d RACDBTo stop named instances:> srvctl stop instance -d RACDB -i racinst1Summary:-Few guidelines for using SRVCTL in Real Application Clusters Always use SRVCTL from the Oracle_home of the database that you are administering. Only run one SRVCTL command at a time for each database, service, or other object, because SRVCTL does not support concurrent executions of commands on the same object. To change your oracle RAC database configuration, log in to the database as the oracle user.srvctl most common and usefull commandssrvctl start database d database-namesrvctl stop database d database-namesrvctl start asm n node-namesrvctl stop asm n node-namesrvctl start nodeapps n node-namesrvctl stop nodeapps n node-namesrvctl status service -d-s