ASM (AUTOMATIC STORAGE MANAGEMENT)

 

Automatic Storage Management (ASM) simplifies administration of Oracle related files by allowing the administrator to reference disk groups rather than individual disks and files, which are managed by ASM. The ASM functionality is an extension of the Oracle Managed Files (OMF) functionality that also includes striping and mirroring to provide balanced and secure storage. The new ASM functionality can be used in combination with existing raw and cooked file systems, along with OMF and manually managed files.

The ASM functionality is controlled by an ASM instance. This is not a full database instance, just the memory structures and as such is very small and lightweight.

The main components of ASM are disk groups, each of which comprise of several physical disks that are controlled as a single unit. The physical disks are known as ASM disks, while the files that reside on the disks are know as ASM files. The locations and names for the files are controlled by ASM, but user-friendly aliases and directory structures can be defined for ease of reference.

         Disks

Disk groups are created using the CREATE DISKGROUP statement. This statement allows you to specify the level of redundancy:

• NORMAL REDUNDANCY - Two-way mirroring, requiring two failure groups.
• HIGH REDUNDANCY - Three-way mirroring, requiring three failure groups.
• EXTERNAL REDUNDANCY - No mirroring for disks that are already protected using hardware mirroring or RAID.

HOW TO CREATE DISK GROUPS:

CREATE DISKGROUP NEW_GROUP NORMAL REDUNDANCY

    '/dev/raw/raw6' NAME d6,

    '/dev/raw/raw7' NAME d7,

HOW TO DROP DISK GROUP:

DROP DISKGROUP NEW_GROUP  INCLUDING CONTENTS;

HOW TO ADD DISK TO A GROUP

ALTER DISKGROUP NEW_GROUP ADD DISK

  '/dev/raw/raw8';

HOW TO DROP A DISK

ALTER DISKGROUP NEW_GROUP DROP DISK d7;

        ASM Views

The ASM configuration can be viewed using the V$ASM_% views, which often contain different information depending on whether they are queried from the ASM instance, or a dependent database instance.

V$ASM_ALIAS, V$ASM_CLIENT, V$ASM_DISK, V$ASM_DISKGROUP, V$ASM_FILE, V$ASM_OPERATION

V$ASM_TEMPLATE