Configuring Databases Using Soft Links
When you specify the location for the storage objects of any relational database management system (RDBMS), there are two options; soft or absolute paths. A soft path, also referred to as a symbolic path, is a file name that links to the physical file through symbolic links (ln -s). An absolute path represents the physical file itself. Physical files can be file system files, raw devices, or VERITAS Volume Manager, Solstice DiskSuite™ software, or Solaris™ Volume Manager volumes.
This Sun BluePrints™ OnLine article explains the advantages of using soft links when configuring databases and provides techniques and examples for using them. It contains the following sections:
"Benefits of Using Soft Links"
"Using Symbolic Links to Set Up a Database"
"Using Soft Links With VERITAS QIO"
Benefits of Using Soft Links
Using an absolute file path to specify the location of database storage objects permanently ties the database object to its physical location. There are a number of situations, in a benchmark or production environment, where it's desirable to have the flexibility to quickly and safely alter the location of database objects.
The following sample situations demonstrate instances where the use of symbolic links are beneficial:
Relocating a complete database to a different input/output (I/O) subsystem.
To relocate a database, simply copy the database files to their new storage location and reestablish the links between the database files and that new storage location.
When the underlying I/O layout for ORACLE™ storage objects (dbf files) become a bottleneck, you can relocate the objects as described in the preceding bullet.
Validating a database with a cold backup.
Once a backup copy of a database is in place, you can simply change the current database links to point to the backed up database area and then bring up the backup database to quickly confirm that the backup is valid.
Ease of database management when VERITAS file system (VxFS) is deployed with VERITAS QuickIO (VERITAS QIO). For more information, read "Using Soft Links With VERITAS QIO" on page 4.
Symbolic links provide meaningful naming for raw devices used in database configurations; for example, when $ORACLE_BASE/oradta/PROD/system.dbf is used instead of the actual raw partition /dev/rdsk/c1t1d0s3. This can simplify database management and configuration tasks.
These benefits come with some added complexity. You must have foresight when adding a new database file. There is no tolerance for errors between the database reference and the symbolic-link name. An error could result in the symbolic-link file system being inadvertently filled.