ASM is Oracle’s solution to manage the File System + Volume Manager .
Why ASM
Before the ASM, Oracle support RAW device and file system.
RAW device has better performance however, once the file is being created at raw device, it can not be renamed and adjust the device size. Therefore, Oracle has ASM to have the RAW device’s performance and File system’s flexibility.
ASM
- ASM is composite by ASM disk groups and ASM instance.
- The ASM instance is a individual instance and mange the ASM disk groups.
- The ASM instance can be shared by multiple Oracle instances.
- The ASM disk groups can be shared by ASM instances ( In the RAC environment ).
Connect to the ASM instance
connect as sysdba or as sysasm
Connect to the database instance. Because the DB files are managed by ASM, the files only show the diskgroups.
DISK GROUPS
Each disk group is composite by one or more disks. All file on the disk group are distribute among all the disks belong the disk group .
- Coarse striping
- File striping
- Failover group
- Allocation unit : min 1 MB
ASMCA ( ASM configuration Assistant )
We can use ASMCA to create/mount/drop disk group and add disk to the disk group.
However, to remove the disk from disk group, we have to use sql statement .
ASMCA
CREATE DISK GROUP
Drop disk from disk group
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