ASM ( Automatic Storage Management )

1. ASM stands for Automatic Storage Management.

2. it's providing Automatic Load Balancing overall Availiable disk ,it reduce the hot spot in file system,it prevents fragementation of Disks.

3.  it does Stripping and Mirroing  to increase relaiability and performance.

4. An ASM instance does not have it's own datafiles like a regular oracle  database.

5. A single ASM instances can manage all oracle database instance on that server
             CSS background process should be up and running to maintain ASM instances and database.

6. Manditory parameter pfile or spfile in ASM instance.

    instance_type=ASM
    instance_name=+ASM
    asm_diskstring=/dev/sda1,/dev/sda2
    asm_power_limit=2
    asm_diskgroup=DATA

7. asm_power_limit

       * it repreasents max. speed of asm instance during a rebalancing disk.
       * values = 1 to 11 ( by default 2 in ASM )

8. ASM instances uses several background processes like SMON,PMON,RBAL,ARBN,ASMB.........

   * RBAL - coordinate the disk activity

  * ASMB - coordinate the instance and database instance;

 * ARBN - process performs rebalancing work which can include moving data extends.


How to create a disk in disk group:

SQL> create diskgroup DATA disk '/dev/sda3';


how to ADD a disk in diskgroup:

SQL>alter diskgroup DATA add disk '/dev/sda5','/dev/sda6';


how to Check ASM disk :

SQL>select name,header_status,path,disk_number,free_mb,total_mb from v$asm_disk;



                                                Thank you