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ASM Template Tips

Oracle Database Tips by Donald BurlesonJanuary 29, 2013

Question:  Can you explain how the Oracle ASM diskgroup templates work?  I understand that a template can be attached to a disk group by I do not understand when you use the "alter diskgroup xxx add template" command, when the template is used.

Answer:  In plain English, an ASM template is a collection of attributes that can be created and deployed to multiple diskgroups.  The attributes within the definition in an ASM diskgroup are applied when you create data files within the diskgroup, and the attributes apply to the data files.

Collections of attributes used by ASM during file creation are known as templates. Templates are used to simplify ASM file creation by mapping complex file attribute specifications into a single named object (template). Each Oracle file type has its own default template. Each disk group contains its own set of definition templates. Template names only have to be unique within a single ASM disk group, a template of the same name can exist in different disk groups with each separate template having their own unique properties.

Prior to Oracle 10g you were forced to use the "add template" syntax to add attributes to an ASM diskgroup, whereas in 11g and beyond the "template" command is superseded by the "add attribute" command.

Here is a list of the "default" (built-in) templates and their attributes:

Template name Striping Mirroring when using a normal redundancy disk group Mirroring when using a high redundancy disk group Mirroring when using an external redundancy disk group
Controlfile Fine 3-Way Mirroring 3-Way Mirroring No Mirroring
Datafile Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Onlinelog Fine 2-Way Mirroring 3-Way Mirroring No Mirroring
Archivelog Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Tempfile Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Backupset Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Parameterfile Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Dataguardconfig Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Flashback Fine 2-Way Mirroring 3-Way Mirroring No Mirroring
Changetracking Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Dumpset Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Xtransport Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring
Autobackup Coarse 2-Way Mirroring 3-Way Mirroring No Mirroring

In addition to these "named" templates you can also create user-defined templates.  These user-defined templates appear in the "name" column of the v$asm_template view.

When you first create a diskgroup, Oracle creates a "default" template.  This default template includes attributes such as the type of mirroring (2-way or 3-way) and whether the data files are to be coarse or fine striped:

alter diskgroup
add template
   (mirror, fine);

Administrators can change the attributes of the default templates or add their own templates. This lets an administrator specify the appropriate file creation attributes as a template. However, if a DBA needs to change an ASM file attribute after a file has been created, then the file must be copied using RMAN into a new file created with a different template that contains the new attributes.

When you create a disk group, Oracle creates system default template for the disk group. It includes default attributes for various file types like control files or data files. The DBA can mention whether the files created via the template should be 2-way or 3-way mirrored and Coarse or fine striped.

The "add template" syntax is optional and if you do not assign a template to a diskgroup, Oracle will apply a default template for you.

There is a v$asm_attribute view to support ASM template attributes:



order by

The v$asm_template has group_number and v$asm_attribute has group_number, and this supports that each template group may have many attributes.


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