Oracle File types

Database files are important to a storage administrator, because you normally do not want to backup the database files with your standard utilities, so you need to know what they are, and also some small database administration files are very important, so you need to know what they are and how to handle them. The different types of file that comprise an Oracle database and its supporting data include:

In Oracle file terminology, data is stored logically in tablespaces and physically in datafiles. A tablespace is a logical partition that contains both a table and its indexes. Each datafile belongs to only one tablespace but a tablespace can consist of more than one datafile. Database file backups are usually managed by RMAN and so the files should be excluded from standard file system backups. Database file names usually look like sid.DBS.CONTROL.DBF, sid.DBS.DATABASE1.DBF, or sid.DBS.LOG1.DBF. Note that by convention, datafile extensions are .dbf, but this is a convention and can be changed so it is worth checking the file names with your DBA before adding the excludes. You can run several Oracle Database instances on each system, and each instance is identified by a unique 'sid' or system identifier in the filename above

Some Oracle table sizes can run to terrabytes, so partitioning is used to make them easier to manage. Partitioning can be used on tables, indexes, and index-organized tables.
Oracle Database v 19 supports hybrid partitioned tables, which are tables in which some partitions reside in the database and some partitions reside outside the database in external files. These externl files could be operating system files or Hadoop Distributed File System (HDFS) files.

The control file is a binary file that contains the database and log file names. It is impossible to start an Oracle database without a control file, so they are usually replicated - preferably on different disks. If you use Netbackup to backup your databases, it is essential that you know where the current control file is. Control files are usually called controlnn.ctl where n is an integer. You could search for files that follow that pattern, but the only reliable way to identify them is with an SQL query within Oracle. In other words, ask your DBA.

The redo logs contain changed data for wind-forward purposes and the undo logs contain the original data before changes were applied for wind-back purposes. Log file extensions are usually .rdo or .log, Redo and undo log backups are usually managed by RMAN and should be excluded from standard file system backups. A redo log is often called a log group, because there can be two or more mirrored copies of the online redo log files in each group.

Temporary files are used to hold in flight work that is too big to be held in memory. These files cannot be recovered and so do not require backup.

A couple of important system files are:

The Oratab is a colon-delimited text file on Unix and Linux systems that defines the association between ORACLE_SID and ORACLE_HOME variables. This file is held in /etc/oratab
Entries are of the form: $ORACLE_SID:$ORACLE_HOME:<N|Y>:
The first and second fields are the system identifier and home directory of the database respectively. The third field indicates if the database should be brought up at system boot time. For example,

Oracle Storage

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I retired 2 years ago, and so I'm out of touch with the latest in the data storage world. The Lascon site has not been updated since July 2021, and probably will not get updated very much again. The site hosting is paid up until early 2023 when it will almost certainly disappear.
Lascon Storage was conceived in 2000, and technology has changed massively over those 22 years. It's been fun, but I guess it's time to call it a day. Thanks to all my readers in that time. I hope you managed to find something useful in there.
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