Introduction Oracle Automatic Storage Management(ASM)

Introduction Oracle Automatic Storage Management(ASM)

Oracle ASM is a volume manager and file system for Oracle database files that support single instance or RAC.
ASM has similar architecture like Oracle instance. ASM instances mount disk groups to make oracle ASM files available to database instances.
Oracle ASM manages Metadata about diskgroups information : disk that belong to diskgroup, amount of space available in Dg, file names, location,advm volume manger.

Oracle ACFS (ASM Cluster File system) and Oracle ADVM (Oracle ASM Dynamic Volume Manager) are key components of Storage Management.
BOTH Oracle ACFS and ADVM has extend the functionality of Oracle ASM.
Oracle ACFS to support all customers files.
ADVM provides volume management services and standard disk devices driver interface to clients.

ASM components
ASM –> Disk groups –> ASM files –> Extents –> Allocation units.

Disk Groups
Disk group is collection of disks that manages as a Unit. The content in file is stored distributed to provide uniform performance and eliminate hot spots.
You can add or remove the disks from diskgroup while database continue to access files.

Files
File belong to one diskgroup. It is used to store the information.

Allocation Unit
Oracle ASM disk is divided into allocation units (AU). An allocation unit is the fundamental unit of allocation within a disk group.

Extent
Each extent resides on an individual disk. Extents consist of one or more allocation units (AU).

Features of Oracle ASM

Oracle ASM Mirroring
Mirroring protects data integrity by storing copies of data on multiple disks
ASM provide mirroring options:
External redundancy disk groups enable external redundancy that you use disk has redundancy capability. Do not use failure groups.
Normal redundancy disk groups enable two way mirroring. Normal redundancy disk groups require at least two failure groups.
High redundancy disk groups enable three way mirroring. High redundancy disk groups require at least three failure groups

Oracle ASM Striping
Striping has two primary purposes: balance loads across all of the disks in a disk group and reduce I/O latency.
Two type of Stripping:
COARSE-grained striping provides load balancing for disk groups.
FINE-grained striping reduces latency for certain file types by spreading the load more widely.

Note:
1. If Oracle ASM instance fail then connected all database is failed to serve.
2. Oracle Flex ASM configuration, Oracle 12c database instances would not fail. They access another Oracle ASM instance remotely on another node.
3. No need of RAC licence in sharing ASM shared pool with ORacle Cluster-ware.

Discover disk on ASM Startup
ASM_DISKSTRING initialization parameter value to specify its discovery strings.

Rebalance operation
Oracle ASM automatically initiates a rebalance after storage configuration changes,such as when you add, drop, or resize disks.
The power setting parameter determines the speed with which rebalancing operations occur.
ASM_POWER_LIMIT Parameter use to minimize the impact on database performance.

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