Common concepts of ASM

 

30. Start and close the ASM instance
The ASM instance runs similar to other databases, but the default startup mount command is used instead of the startup command. In addition, we can also use startup restrict to temporarily prevent database instances from connecting to the ASM instance and installing the disk group. If people use the shutdown command on the ASM instance, they will wait until all related databases are shut down before the ASM completes the shutdown operation. The only exception is that if shutdown abort is used, the ASM instance does not send the abort command to the relevant database, but all relevant databases will immediately execute a shutdown abort command.

31. ASM dynamic performance View
There are some new dynamic performance views related to the ASM instance. The contents of these views are different in the ASM instance and database instance, as shown in the following table:

View	Content in the ASM instance	Content in RDBMS instances
V $ asm_disk	No Disk found by the ASM instance is recorded in a row, whether or not used for the disk group	Each row records each disk used by the instance.
V $ asm_diskgroup	Each row records information about a disk group, including the general characteristics of the disk group.	Each row records each disk group used, whether or not it has been installed
V $ asm_file	Each row records every file in each installed disk group.	Unused
V $ asm_operation	Each row records a long-running operation in the ASM instance.	Unused
V $ asm_template	Each row records a template in each installed disk group in the ASM instance.	Each row records a template in each installed disk.
V $ asm_client	Each row records each database of each disk group managed by the ASM instance.	If any ASM file is opened, add a line for the ASM instance.
V $ asm_alias	There is no line to record every alias of each installed disk group	Unused

32. ASM file name
All ASM files are OMF, so you do not need to worry about the actual file name used in most management work. When objects are deleted from an ASM disk, the corresponding files are also deleted. The ASM file can be in 6 different formats
1) Full name
Example: + dsg1/ora10g/datafile/system.264.584793233
In the preceding example, the disk group name is + dsg1, and the database name is ora10g. It is a data file in the system tablespace, and the file number/implementation (incarnation) corresponds to 264.584793233.
2) number name
The numeric name is only used to reference an existing ASM file. It allows only the disk group name and file number/To be used to correspond to the ASM file. For example, for the above example, The number name is:
+ Dsg1.264.584793233
3) alias
In the ASM instance, we can use alter diskgroup add alias to create a more friendly name for an existing or new ASM file. First, create a directory.
Alter diskgroup data2 add directory '+ data2/redempt ';
Create an alias:
Alter diskgroup data2 add alias '+ data2/redempt/users. dbf'
For '+ data2/rac0/datafile/users3.256.1 ';
4) alias with template
You can only use an alias with a template when creating a new ASM file. The template provides a method and tag to simplify the file type when creating a new ASM file.
5) incomplete names
Incomplete file name formats can be used to create a single file or multiple files. We can only specify the disk group name, and then use a default template based on the file type. For example:
Create tablespace users4 datafile '+ data1 ';
6) incomplete names with templates. You can specify the disk group and Template Name when creating a file. For example:
Create tablespace users4 datafile '+ data1 (tempfile )';
33. Disk Group Structure
A disk group is a group of physical disks managed as a unit. Each ASM disk, as part of the entire disk group, has an ASM disk name, either specified by DBA or automatically assigned when it is assigned to this disk group. Files in a disk are stored on each disk after being strip, which may be processed by coarse stripping or fine stripping. The groove takes 1 MB as the unit. The groove is suitable for OLTP systems used in data warehouse environments or with low parallel processing and maximum response time for each I/O Request (?) In the system template, only controlfile, onlinelog, and flashback are thin strips, while others are coarse strips.
34. invalid combination disk Group Image
Before defining the image processing type of a disk group, you must make the disk a failure group ). A failure group is a part of a resource consisting of multiple active disks in a disk group, such as a disk controller. If it fails, some disks in the disk group will become unavailable. In most cases, the ASM instance does not know the dependency between the hardware and software of a disk. Therefore, unless a disk is explicitly specified to an invalid group, each disk in the disk group belongs to only one of its own failure groups.
After defining the failure group, we can define the image processing of the disk group. The number of available failure groups in a disk group limits the available image types of the disk group. The following figure shows the available types:
1) External redundancy:
External redundancy requires only one failure group, and the disk group is considered unimportant for database operation, or the disk is managed by an external high-availability hardware, such as a RAID Controller.
2) General Redundancy
Common redundancy requires two failure groups to provide dual-path images.
3) high redundancy
High redundancy requires at least three failure groups and three images are provided, even if two of them are invalid, they can still be used.