Database file types

Owned by KrupeshD (Deactivated)
Last updated: Nov 30, 2012Version comment
3 min read

Dbvisit Standby recognises four database file types that are treated differently during creation of the standby database:

  • Regular filesystem files (FS)
  • Filesystem Oracle Managed Files (OMF)
  • ASM files with fully qualified system name (FQSN)
  • ASM aliases (ALIAS)
Regular filesystem files (FS)

These are regular database files that are stored in a filesystem. Example: /oracle/oradata/system.01.dbf


Filesystem Oracle Managed Files (OMF)

Oracle introduced the change to the filename format used for OMF in the second patch set for Oracle 9i Release 1 (9.0.1.2) and also in Oracle9i Release 2 (9.2). Prior to this fix OMF file names had the following format: 
File Type Format 

 File Type 
Format
Example
Datafile
ora_%t_%u.dbf 
ora_tbs1_2ixfh90q.dbf
Tempfile
ora_%t_%u.tmp 
ora_temp1_6dygh80r.tmp
Redo log file
ora_%g_%u.log
ora_1_wo94n2xi.log
Control file
ora_%u.ctl
ora_cmr7t90p.ctl

Where:

     %t is the tablespace name (possibly truncated)

     %u is an eight character string that guarantees uniqueness

     %g is the online redo log file group number

A file was considered OMF if its base file name had:

  • an "ora_" prefix
  • and a ".dbf", ".tmp", ".log" or ".ctl" extension 

The new and current format for OMF file names on Windows and Unix-based systems is: 

 File Type 
Format
Example
Datafile
 o1_mf_%t_%u_.dbf
 o1_mf_tbs1_2ixfh90q_.dbf
Tempfile
 o1_mf_%t_%u_.tmp   
 o1_mf_temp1_6dygh80r_.tmp
Redo log file
 o1_mf_%g_%u_.log  
 o1_mf_1_wo94n2xi_.log
Control file
 o1_mf_%u_.ctl
 o1_mf_cmr7t90p_.ctl

Where:

     %t is the tablespace name (possibly truncated)

     %u is an eight character string that guarantees uniqueness

     %g is the online redo log file group number

A file is now considered OMF if its base file name has:

  • a "o1_mf_" prefix
  • and a ".dbf", ".tmp", ".log", or ".ctl" extension
  • and an "_" character immediately preceding the extension 

Dbvisit Standby recognizes both naming formats ora_* and o1_mf_* as OMF file formats. OMF files should be created and managed by Oracle. Oracle does not recommend creating files with OMF names implicitly as Oracle is not able to recognize these files as an Oracle managed files and will not manage the files accordingly.

ASM files with fully qualified system name (FQSN)

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 path name 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.

ASM aliases (ALIAS)

 

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 file system 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 (tick) 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 (plus), 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