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Considerations for standby databases using ASM

Considerations for Standby Databases using Automatic Storage Management (ASM). Every file created in ASM gets a system-generated filename, otherwise known as a fully qualified filename (FQFN).

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By Arjen Visser
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August 8, 2019
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Considerations for Standby Databases using Automatic Storage Management

Every file created in ASM gets a system-generated filename, otherwise known as a fully qualified filename (FQFN). The fully qualified filename represents a complete pathname in the ASM file system. An example of a fully qualified filename is:

+dgroup2/sample/controlfile/Current.256.541956473

You can use the fully qualified filename to reference (read or retrieve) an ASM file. ASM generates a fully qualified filename upon any request to create a file. A creation request cannot specify a fully qualified filename. Instead, it uses a simpler syntax to specify a file, such as an alias or just a disk group name. ASM then creates the file, placing it in the correct ASM "path" according to file type, and then assigns an appropriate fully qualified filename. If you specify an alias in the creation request, ASM also creates the alias so that it references the fully qualified filename.

FQFN are generally long and awkward, therefore, to make file-naming convention easier to remember the ASM Alias name format was introduced. ASM Aliases are essentially in hierarchical directory format, similar to the filesystem hierarchy. Alias names specify a disk group name, but instead of a file and incarnation number, a user-friendly string name is used.

Alias ASM filenames, otherwise known as aliases, can be used both for referencing existing ASM files and for creating new ASM files. Alias names start with the disk group name preceded by a plus sign, after which you specify a name string of your choosing. Alias filenames are implemented using a hierarchical directory structure, with the slash (/) or backslash (\) character separating name components. You can create an alias in any system-generated or user-created ASM directory. You cannot create an alias at the root level (+), however.

When you create an ASM file with an alias filename, the file is created with a fully qualified name, and the alias filename is additionally created. You can then access the file with either name.

Alias ASM filenames are distinguished from fully qualified or numeric names because they do not end in a dotted pair of numbers. An example of ASM alias for the fully qualified filename above is:

+ dgroup2/sample/controlfile/control01.dbf

Standby™️ currently creates an ASM standby database using aliases for standby database files. If the primary database uses ASM files that do not have aliases defined for them, just FQFN, Standby™️ will prompt you to provide aliases for the standby ASM datafiles. All ASM standby database files will be created with system-generated FQFN and have aliases defined for them. Aliases for standby datafiles, tempfiles, controlfiles and redo logs will be used in the database dictionary.

To use Standby™️ to create an ASM standby database or a standby database for an ASM primary database, make sure that the operating system user that runs Standby™️ has access to Oracle executables in the ORACLE HOME for the ASM instance. Standby™️ needs execute privilege on the ASMCMD utility, and if your installation implements Oracle 11g grid infrastructure under its own home and user, you may need to add the Standby™️ user to the operating group “oinstall” to make sure it can run the ASMCMD utility.

For a step by step guide, watch our demo:

Arjen Visser
Arjen Visser


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