5 Administering ASM Files, Directories, and Templates

Single File Creation Request

A single file creation request is a request to create a single file, such as a datafile or a control file. The form of the ASM filename in this type of request is either an alias (such as +dgroup2/control/ctl.f) or a disk group name preceded by a plus sign. You use the alias or disk group name where a filename is called for in a statement, such as CREATE TABLESPACE or CREATE CONTROLFILE.

Multiple File Creation Request

A multiple file creation request is a request that can occur multiple times to create an ASM file. For example, if you assign a value to the initialization parameter DB_CREATE_FILE_DEST, you can issue a CREATE TABLESPACE statement (without a filename specification) multiple times. Each time, ASM creates a different unique datafile name.

One form of the ASM filename to use in this type of request is an incomplete filename, which is just a disk group name preceded by a plus sign. In this case, you set DB_CREATE_FILE_DEST to an incomplete filename (for example, +dgroup2), and whenever a command is executed that must create a database file in DB_CREATE_FILE_DEST, the file is created in the designated disk group and assigned a unique fully-qualified name. You can use an incomplete filename in other *_DEST initialization parameters.

Fully-qualified ASM Filename

This form of ASM filename can be used for referencing existing ASM files. It is the filename that ASM always automatically generates when an ASM file is created.

A fully-qualified filename has the following form:

+group/dbname/file_type/file_type_tag.file.incarnation

Where:

• +group is the disk group name preceded by a plus sign.

  You can think of the plus sign (+) as the root directory of the ASM file system, similar to the slash (/) on UNIX or Linux computers.

• dbname is the DB_UNIQUE_NAME of the database to which the file belongs.

• file_type is the Oracle file type and can be one of the file types shown in Table 5-3.

• file_type_tag is type specific information about the file and can be one of the tags shown in Table 5-3.

• file.incarnation is the file/incarnation pair, used to ensure uniqueness.

An example of a fully-qualified ASM filename is:

+dgroup2/sample/controlfile/Current.256.541956473

Numeric ASM Filename

The numeric ASM filename can be used for referencing existing files. It is derived from the fully-qualified ASM filename and takes the form:

+group.file.incarnation

Numeric ASM filenames can be used in any interface that requires an existing file name.

An example of a numeric ASM filename is:

+dgroup2.257.541956473

Alias ASM Filenames

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 filenames or numeric filenames because they do not end in a dotted pair of numbers. It is an error to attempt to create an alias that ends in a dotted pair of numbers. Examples of ASM alias filenames are:

Oracle Database references database files by their alias filenames, but only if you create the database files with aliases. If you create database files without aliases and then add aliases later, the database references the files by their fully-qualified filenames. The following are examples of how the database uses alias filenames:

• Alias filenames appear in V$ views. For example, if you create a tablespace and use an alias filename for the datafile, the V$DATAFILE view shows the alias filename.

• When a control file points to datafiles and online redo log files, it can use alias filenames.

• The CONTROL_FILES initialization parameter can use the alias filenames of the control files. The Database Configuration Assistant (DBCA) creates control files with alias filenames.

CREATE UNDO TABLESPACE myundo 
     DATAFILE '+dgroup3(my_undo_template)/myfiles/my_undo_ts' SIZE 200M; 

ALTER DISKGROUP dgroup3 DROP FILE '+dgroup3/myfiles/my_undo_ts';

Alias ASM Filename with Template

An alias ASM filename with template is used only for ASM file creation operations. It has the following format:

+dgroup(template_name)/alias

Alias filenames with template behave identically to alias filenames. The only difference is that a file created with an alias filename with template receives the mirroring and striping attributes specified by the named template. The template must belong to the disk group that the file is being created in.

The creation and maintenance of ASM templates is discussed in "Managing Disk Group Templates".

An example of an alias ASM filename with template is:

+dgroup1(my_template)/config1

Explicitly specifying a template name, as in this example, overrides the system default template for the type of file being created.

Incomplete ASM Filename

Incomplete ASM filenames are used only for file creation operations and are used for both single and multiple file creation. They consist only of the disk group name. ASM uses a system default template to determine the ASM file mirroring and striping attributes. The system template that is used is determined by the file type that is being created. For example, if you are creating a datafile for a tablespace, the datafile template is used.

An example of using an incomplete ASM filename is setting the DB_CREATE_FILE_DEST initialization parameter to:

+dgroup1

With this setting, every time you create a tablespace, a datafile is created in the disk group dgroup1, and each datafile is assigned a different fully-qualified name. See "Creating ASM Files Using a Default Disk Group Specification" for more information.

Incomplete ASM Filename with Template

Incomplete ASM filenames with templates are used only for file creation operations and are used for both single and multiple file creation. They consist of the disk group name followed by the template name in parentheses. When you explicitly specify a template in a file name, ASM uses the specified template instead of the default template for that file type to determine mirroring and striping attributes for the file.

An example of using an incomplete ASM filename with template is setting the DB_CREATE_FILE_DEST initialization parameter to:

+dgroup1(my_template)

Creating ASM Files Using a Default Disk Group Specification

Using the Oracle Managed Files feature for operating system files, you can specify a directory as the default location for the creation of datafiles, temporary files, redo log files, and control files. Using the Oracle Managed Files feature for ASM, you can specify a disk group, in the form of an incomplete ASM filename, as the default location for creation of these files, and additional types of files, including archived log files. As for operating system files, the name of the default disk group is stored in an initialization parameter and is used whenever a file specification (for example, DATAFILE clause) is not explicitly specified during file creation.

The initialization parameters in Table 5-4 accept the multiple file creation context form of ASM filenames as a destination:

The initialization parameters in Table 5-5 accept the multiple file creation context form of the ASM filenames and ASM directory names as a destination:

The following example illustrates how an ASM file, in this case a datafile, might be created in a default disk group.

DB_CREATE_FILE_DEST = '+dgroup1'

CREATE TABLESPACE tspace1;

Using ASM Filenames in SQL Statements

You can specify ASM filenames in the file specification clause of your SQL statements. If you are creating a file for the first time, use the creation form of an ASM filename. If the ASM file already exists, you must use the reference context form of the filename, and if you are trying to re-create the file, you must add the REUSE keyword. The space will be reused for the new file. This usage might occur when, for example, trying to re-create a control file, as shown in "Creating Control Files in ASM".

If a reference context form is used with the REUSE keyword and the file does not exist, an error results.

Partially created files resulting from system errors are automatically deleted.

CREATE TABLESPACE  tspace2 DATAFILE '+dgroup2' SIZE 200M AUTOEXTEND ON;

Adding an Alias Name for an ASM Filename

Use the ADD ALIAS clause of the ALTER DISKGROUP statement to create an alias name for an ASM filename. The alias name must consist of the full directory path and the alias itself.

ALTER DISKGROUP dgroup1 ADD ALIAS '+dgroup1/mydir/second.dbf'
     FOR '+dgroup1/sample/datafile/mytable.342.3';

ALTER DISKGROUP dgroup1 ADD ALIAS '+dgroup1/mydir/second.dbf'
     FOR '+dgroup1.342.3';

Renaming an Alias Name for an ASM Filename

Use the RENAME ALIAS clause of the ALTER DISKGROUP statement to rename an alias for an ASM filename. The old and the new alias names must consist of the full directory paths of the alias names.

ALTER DISKGROUP dgroup1 RENAME ALIAS '+dgroup1/mydir/datafile.dbf'
     TO '+dgroup1/payroll/compensation.dbf';

Dropping an Alias Name for an ASM Filename

Use the DROP ALIAS clause of the ALTER DISKGROUP statement to drop an alias for an ASM filename. The alias name must consist of the full directory path and the alias itself. The underlying file to which the alias refers is unchanged.

ALTER DISKGROUP dgroup1 DROP ALIAS '+dgroup1/payroll/compensation.dbf';

ALTER DISKGROUP dgroup1 
     DROP ALIAS '+dgroup1/sample/datafile/mytable.342.3';

Dropping Files and Associated Aliases from a Disk Group

You can delete ASM files and their associated aliases from a disk group using the DROP FILE clause of the ALTER DISKGROUP statement. You must use a fully-qualified filename, a numeric filename, or an alias name when specifying the file that you want to delete. The underlying file on the file system is not dropped when the alias is dropped.

Some reasons why you might need to delete files include:

• A file created using aliases is not an Oracle Managed File. Consequently, it is not automatically deleted.

• A point-in-time-recovery of a database might restore the database to a time before a tablespace was created. The restore does not delete the tablespace, but there is no reference to the tablespace or its datafile in the restored database. You could manually delete the datafile.

ALTER DISKGROUP dgroup1 DROP FILE '+dgroup1/payroll/compensation.dbf';

ALTER DISKGROUP dgroup1
     DROP FILE '+dgroup1/sample/datafile/mytable.342.372642';

Inside /sys/asm

The ASM virtual folder is created by default during XML DB installation. If the database is not configured to use ASM, the folder is empty and no operations are permitted on it.

The ASM virtual folder contains folders and subfolders that follow the hierarchy defined by the structure of an ASM fully-qualified file name. Figure 5-1 show this hierarchy, which for simplicity, excludes directories created for aliases.

The folder /sys/asm contains one subfolder for every mounted disk group, and each disk group folder contains one subfolder for each database that uses the disk group. In addition, a disk group folder might contain files and folders corresponding to aliases created by the administrator. Continuing the hierarchy, the database folders contain file type folders, which contain the ASM files.

Figure 5-1 Hierarchal Structure of ASM Folders

Description of "Figure 5-1 Hierarchal Structure of ASM Folders"

Sample FTP Session

In the following sample FTP session, the disk groups are DATA and RECOVERY, the database name is MFG, and dbs is a directory that was created for aliases. All files in /sys/asm are binary.

Creating a New Directory

Use the ADD DIRECTORY clause of the ALTER DISKGROUP statement to create a hierarchical directory structure for alias names for ASM files. Use the slash character (/) to separate components of the directory path. The directory path must start with the disk group name, preceded by a plus sign (+), followed by any subdirectory names of your choice.

The parent directory must exist before attempting to create a subdirectory or alias in that directory.

ALTER DISKGROUP dgroup1 ADD DIRECTORY '+dgroup1/mydir'; 

ALTER DISKGROUP dgroup1
     ADD DIRECTORY '+dgroup1/mydir/first_dir/second_dir';

Renaming a Directory

The RENAME DIRECTORY clause of the ALTER DISKGROUP statement enables you to rename a directory. System created directories (those containing system-generated names) cannot be renamed.

ALTER DISKGROUP dgroup1 RENAME DIRECTORY '+dgroup1/mydir'
     TO '+dgroup1/yourdir';

Dropping a Directory

You can delete a directory using the DROP DIRECTORY clause of the ALTER DISKGROUP statement. You cannot drop a system created directory. You cannot drop a directory containing alias names unless you also specify the FORCE clause.

ALTER DISKGROUP dgroup1 DROP DIRECTORY '+dgroup1/yourdir' FORCE;

Template Attributes

Table 5-6 shows the permitted striping attribute values and Table 5-7 shows the permitted redundancy values for ASM templates. These values correspond to the STRIPE and REDUND columns of V$ASM_TEMPLATE.

Adding Templates to a Disk Group

To add a template to a disk group, use the ADD TEMPLATE clause of the ALTER DISKGROUP statement. You specify the name of the template, its redundancy attribute, and its striping attribute.

The syntax of the ALTER DISKGROUP command for adding a template is as follows:

ALTER DISKGROUP disk_group_name ADD TEMPLATE template_name 
  ATTRIBUTES ([{MIRROR|HIGH|UNPROTECTED}] [{FINE|COARSE}]);

Both types of attribute are optional. If no redundancy attribute is specified, the value defaults to MIRROR for a normal redundancy disk group, HIGH for a high redundancy disk group, and UNPROTECTED for an external redundancy disk group. If you do not specify a striping attribute, then the value defaults to COARSE.

ALTER DISKGROUP dgroup2 ADD TEMPLATE reliable ATTRIBUTES (HIGH FINE);

ALTER DISKGROUP dgroup2 ADD TEMPLATE unreliable ATTRIBUTES (UNPROTECTED);

Modifying a Disk Group Template

The ALTER TEMPLATE clause of the ALTER DISKGROUP statement enables you to modify the attribute specifications of an existing system default or user-defined disk group template. Only specified template properties are changed. Unspecified properties retain their current value. When you modify an existing template, only new files created by the template reflect the attribute changes. Existing files maintain their attributes.

ALTER DISKGROUP dgroup2 ALTER TEMPLATE reliable 
     ATTRIBUTES (COARSE);

Dropping Templates from a Disk Group

Use the DROP TEMPLATE clause of the ALTER DISKGROUP statement to drop one or more templates from a disk group. You can only drop templates that are user-defined; you cannot drop system default templates.

ALTER DISKGROUP dgroup2 DROP TEMPLATE unreliable;

Creating Tablespaces in ASM: Specifying Redundancy and Striping with Templates

Use the SQL ALTER SYSTEM and CREATE TABLESPACE statements to create a tablespace that uses a user-defined template to specify the redundancy and striping attributes of the datafile.

ALTER SYSTEM SET DB_CREATE_FILE_DEST = '+dgroup1(my_template)';

CREATE TABLESPACE tspace3;