Oracle 19c - Oracle 19c RAC | Real Application Clusters (RAC) Technical Architecture Overview- Part5
Part1: https://www.youtube.com/watch?v=nQEn3... Part2: https://www.youtube.com/watch?v=w3Kmx... Part3: https://www.youtube.com/watch?v=sT2mk... Part4: https://www.youtube.com/watch?v=nW9zn... Oracle Automatic Storage Management(ASM) Configurations: All ASM installations can be configured to serve Oracle ASM Flex Clients. On the left, Hub Node 1 is the traditional Standalone configuration with the ASM instance local to the database instance. In the past this was the only configuration available. Each node had to have an ASM instance, if ASM was used to provide shared storage. Notice that Hub node 2, is an ASM client node. It uses the ASM service on hub node 3, another node in the cluster, to access the metadata, and then does direct access to ASM disk storage for the data blocks. To the right, is hub node 5. It has no direct access to the ASM disk storage, but gets all the data through the IO Server (IOS) on hub node 4. The Oracle IO Server was introduced in Oracle Grid Infrastructure version 12.2. IOS enables you to configure client clusters on such nodes. On the storage cluster, clients send their IO requests to network ports opened by an IOServer. The IOServer instance receives data packets from the client and performs the appropriate IO to Oracle ASM disks similar to any other database client. On the client side, databases can use dNFS to communicate with an IOServer instance. However, there is no client side configuration so you are not required to provide a server IP address or any additional configuration information. On nodes and clusters that are configured to access Oracle ASM files through IOServer, the discovery of the Oracle IOS instance occurs automatically. Each ASM instance in a cluster has access to the ASM disk storage in that cluster. ASM disks are shared disks attached to the nodes of the cluster, in possibly varying ways, as shown in the graphic. ASM manages Disk Groups rather than individual disks. The ASM utilities allow you to add disks, partitions, logical volumes or Network attached files (NFS) to a disk group. ASM Instance: Every time ASM or a database is started, a shared memory area called the System Global Area (SGA) is allocated and the ASM background processes are started. However, because ASM performs fewer tasks than a database, an ASM SGA is much smaller than a database SGA. The combination of background processes and the SGA is called an Oracle ASM instance. The instance represents the CPU and RAM components of a running ASM environment. The SGA in an ASM instance is different in memory allocation and usage than the SGA in a database instance. The SGA in the ASM instance is divided into four primary areas as follows: Shared Pool: Used for metadata information Large Pool: Used for parallel operations ASM Cache: Used for reading and writing blocks during rebalance operations Free Memory: Unallocated memory available The minimum recommended amount of memory for an ASM instance is 256 MB. Automatic memory management is enabled by default on an ASM instance and will dynamically tune the sizes of the individual SGA memory components. The amount of memory that is needed for an ASM instance will depend on the amount of disk space that is being managed by ASM. The second part of the ASM instance is the background processes. An ASM instance can have many background processes; not all are always present. Because the ASM instance shares the same code base as an Oracle database instance, all the required background processes of a database instance will exist in the ASM instance. There are required background processes and optional background processes. Some of these processes may include the following: Hope this helps! Cheers! Ramesh.
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