Oracle 10g R2 create ASM instance Step By Step

ASM concepts

1. what is Automatic Storage Management (ASM, it is a disk management tool that can implement strip, image data files, recovery files, and other files among multiple physical devices. The distribution unit is AUs (allocation units) the balance is distributed across all disks in the disk group. ASM uses the index technology to track the positions of each AUs and supports the dynamic increase and decrease of online disks. When the disk changes, AUs automatically re-implements Dynamic Distribution and supports RAC cluster technology. An ASM instance runs on each node. Point-to-point communication between ASM instances is a software-only implementation method, third-party RAID works at the volume level and uses the uniform strip size. ASM can work at the file level, and different files can use different strip sizes.

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2. Advantages of ASM

Disk increase: it is very easy to add disks. No downtime is required and the file area is automatically reassigned.

I/O allocation: I/O is automatically distributed across all available Disks without manual intervention. This reduces the possibility of hot spots.

Band Width: segments in the redo log file can be subdivided (K for faster transmission rate). For data files, the band width is slightly larger (MB, to transmit a large number of data blocks at a time ).

Buffer: the ASM file system directly performs input/output without buffering.

Image: If the hardware image is unavailable, you can easily create a software image.

Core asynchronous I/O: to implement core asynchronous I/O, no special settings are required, and no original or third-party file systems (such as Veritas Quick I/O) are required)

3. RAID level of common Oracle data files

SYSTEM and UNDO tablespaces are usually placed on RAID 1 volumes.

Online redo logs are usually placed on RAID 0 volumes.

Control files are usually placed on RAID 0 + 1 volumes.

Data files are usually placed on RAID 5 volumes.

4. the ASM architecture (mainly composed of an ASM instance and an ASM disk group) creates an ASM instance for managing the ASM disk group. The ASM disk is composed of an ASM disk, one or more ASM disks can be actual disks, partitions of a disk, or logical volumes managed by LVM, however, the size of the unformatted raw device ASM disk group must be the sum of the size of the ASM disk in the group. The available capacity varies depending on the fault tolerance level.

5. ASM instance and RDBMS instance

The ASM instance is similar to a common database instance (RDBMS) and also consists of SGA and a bunch of background processes. For most systems, the LargePool In the ASM instance is used to store the Extent Map in 64 MB, the LargePool size can be calculated based on the database size. Generally, the size of GB needs to be 1 MB to store Extent Map. A common RDBMS instance will locate the data file and open its data file, in a database stored in ASM, the job is taken over by the ASM instance, that is, the ASM instance is used to locate and manage the ASM disk and disk group. The ASM instance has background processes similar to common RDBMS instances, such as SMON, PMON, LGWR, DBWR, and CKPT. Two new processes are added: RBAL and ARBn RBAL: ARBn is used to coordinate and manage the dynamic balance between disk groups. It can be multiple. The mobile ASM instance used to complete the AU is only used to locate and manage the ASM disk and cannot load or open the database, therefore, you cannot read the data dictionary information. Generally, an ASM instance has a parameter. You can only use the password file or operating system authentication as sysdba or sysoper to start or close the instance. An ASM instance can provide services for multiple RDBMS instances. Multiple ASM instances can be created on one host. However, an ASM instance is usually used on one host. If one instance serves multiple RDBMS instances, we recommend that you separate ASM_HOME of ASM from ORACLE_HOME of DB, the creation and configuration of the ASM disk group can be easily upgraded and maintained in the future. After the ASM instance is started, the RDBMS instance that uses the ASM disk is the same as the common RDBMS instance, but there are two more background processes, RBAL, ASMB. ASMB uses a server process such as oracle + ASM1 to establish a session between a common RDBMS instance and the ASM instance, and transmits information about disk files. RBAL opens the ASM disk located through the ASM instance. Note: the ASM instance does not replace the RDBMS instance to read or write data files. Data is transmitted directly on the ASM disk and RDBMS instance. The ASM instance is only used to locate the asm disk where the data file is located, disk Area and required information. If a new data file is added, RDBMS informs the ASM instance to create a data file, and the ASM instance allocates a disk area.

(Extent), and create a disk region ing address and return it to the RDBMS instance. Then, the RDBMS writes data directly to the disk group.

6. File Types stored in the ASM instance

Control file parameter file online log file archive log file data file temporary file RMAN backup set, image copy control file backup set datapump dump file, Change Tracing file

The next section describes how to create an ASM instance.

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