Create an ASM instance and an ASM Database

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-- Create an ASM instance and an ASM Database

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1. concepts related to ASM

1. What is ASM (Auto Storage Management)

Automatic Storage Management is a tool used to manage disks.

Supports striping, mirror data files, and restore files between multiple physical devices.

Files are evenly distributed across all disks in the disk group according to the allocation unit AUs (allocation units). ASM uses the index technology to track the location of each AUs.

Supports dynamic increase and decrease of online disks. When the disk changes, the AUs automatically implements Dynamic Distribution again.

Supports RAC cluster technology. One ASM instance is run on each node, and point-to-point communication can be achieved between ASM instances.

It is a software-only implementation method. A third-party RAID works at the volume level and uses a uniform strip size. ASM can work at the file level and different files can be used.

Different strip sizes

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. ASM architecture (mainly composed of an ASM instance and an ASM disk group)

To use ASM, you need to create an ASM instance for managing the ASM disk group.

An ASM disk is composed of one or more ASM disks.

An ASM disk can be an actual disk, a partition of a disk, or a logical volume managed by LVM, but must be an unformatted raw device.

The size of the ASM disk group is the total 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, SGA only needs 64 MB.

The LargePool In the ASM instance is used to store the Extent Map. The LargePool size can be calculated based on the database size. Generally, the size of GB needs to be 1 MB for the Extent Map.

A common RDBMS instance locates a data file and opens 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

Manages ASM disks and disk groups.

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: Used to coordinate and manage the dynamic balance between disk groups

ARBn: Multiple ARBn can be used to move the AU

The ASM instance only locates and manages the ASM disk. It cannot load or open the database, and therefore cannot read the data dictionary information.

An ASM instance usually has a parameter. You can only use the password file or operating system authentication as sysdba or sysoper to start or close the instance.

For differences between sysdba and sysoper, see system sys and sysoper sysdba.

An ASM instance can provide services for multiple RDBMS instances. Multiple ASM instances can be created on one host, but an ASM instance is usually used on one host.

If an instance serves multiple RDBMS instances, we recommend that you separate ASM_HOME of ASM from ORACLE_HOME of DB to facilitate future upgrade and maintenance.

Create and configure an ASM disk group after the ASM instance is started.

The RDBMS instance using the ASM disk is the same as the common RDBMS instance, but there are two more background processes, RBAL and ASMB.

ASMB uses a server process such as oracle + ASM1 to establish a session between a common RDBMS instance and an 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 data files.

The asm disk, 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 dumping file, Change Tracing file

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