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ASM metadata file number 7 - volume directory - keeps track of files associated with ASM Dynamic Volume Manager (ADVM) volumes.

An ADVM volume device is constructed from an ASM dynamic volume. One or more ADVM volume devices may be configured within each disk group. ASM Cluster File System (ACFS) is layered on ASM through the ADVM interface. ASM dynamic volume manager is another client of ASM - the same way the database is. When a volume is opened, the corresponding ASM file is opened and ASM extents are sent to the ADVM driver.

There are two file types associated (more...)

The alias directory - ASM file number 6 - provides a hierarchical  naming system for all the files in a disk group.

A system file name is created for every file and it is based on the file type, database instance and type-specific information such as tablespace name. User alias may also be created if a full path name was given when the file was created.

Alias Directory entries include the following fields:

• Alias or directory name
• Alias incarnation number
• File number
• File incarnation number
• Parent directory
• System flag

The ASM alias information is externalised via V$ASM_ALIAS view.

Using the alias

(more...)

The Template Directory - ASM file number 5 - contains information about all file templates for the disk group.

There are two types of templates - system and user created. The default (system) templates are always available for each file type supported by ASM. User created templates can be added for a custom template specifications.

Each template entry contains the following information:

• The template name (for the default templates this corresponds to the file type)
• The file redundancy (defaults to the disk group redundancy)
• The file striping (default is file-type specific)
• The system flag (set for the system templates)

Using (more...)

Some long-running ASM operations, like rebalance, drop disk, create/delete/resize file, cannot be described by a single record in the active change directory. For those operations ASM uses the Continuing Operations Directory (COD) - ASM file number 4. There is one COD per disk group.

If a process performing the long-running operation dies before completing it, a recovery process will look at the entry and either complete or rollback the operation. There are two types of continuing operations - background and rollback.

Background operation

A background operation is preformed by an ASM instance background process. It is done as part of (more...)

When ASM needs to make an atomic change to multiple metadata blocks, a log record is written into the Active Change Directory (ACD), which is ASM metadata file number 3. These log records are written in a single I/O.

ACD is divided into chunks (threads) and each running ASM instance has its own 42 MB chunk. When a disk group is created, a single chunk is allocated for the ACD. As more instances mount that disk group, the ACD grows (by 42 MB) to accommodate every running instance with its own ACD chunk.

The ACD components are:

• ACDC - ACD (more...)

ASM file number 2 - the disk directory - keeps track of all disks in the disk group. As disk groups are independent storage units, each disk group will have its own disk directory.

As far as ASM is concerned, the disk directory is just another file. It has its own entry in the file directory, it is mirrored as per the disk group redundancy policy and it grows as needed.

Each disk directory entry maintains the following information:

• Disk number
• Disk state
• ASM disk name (this can differ from the disk's OS name)
• Fail group name
• Create time-stamp
• Failure time-stamp
• (more...)