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DBA - Storage

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• DBA - Storage
  • Database Storage Architecture
  • Oracle Managed Files

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Database Storage Architecture

• The files that comprise an Oracle database are as follows:

  • Control files:

    • Each database has one unique control file that contains data about the database itself (that is, physical database structure information).
    • Multiple copies may be maintained to protect against total loss.
    • It can also contain metadata related to backups.
    • The control file is critical to the database.
      • Without the control file, the database cannot be opened.

  • A control file is a small binary file that records the physical structure of the database and includes:

    • The database name
    • Names and locations of associated datafiles and online redo log files
    • The timestamp of the database creation
    • The current log sequence number
    • Checkpoint information

  • Data files: .dbf

    • They contain the user or application data of the database, as well as metadata and the data dictionary.
    • A tbspace cannot exist without data file
      • Must have at least one data file.

  • Online redo log files:

    • They allow for instance recovery of the database.
    • If the database server crashes and does not lose any data files, the instance can recover the database with the information in these files.

• The following additional files are used during the operation of the database:

  • Initialization parameter file:

    • Is used to define how the instance is configured when it starts up

  • Password file:

    • Allows users using the SYSDBA, SYSOPER, SYSBACKUP, SYSDG, SYSKM, and SYSASM roles to connect remotely to the instance and perform administrative tasks

  • Backup files:

    • Are used for database recovery.
    • You typically restore a backup file when a media failure or user error has damaged or deleted the original file.

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Oracle Managed Files

• Oracle Managed Files (OMF)

  • eliminates the need for you to directly manage the operating system files in an Oracle database. - specify operations in terms of database objects rather than file names.

• The database internally uses standard file system interfaces to create and delete files as needed for the following database structures:

  • Tablespaces
  • Redo log files
  • Control files
  • Archived logs
  • Block change tracking files
  • Flashback logs
  • RMAN backups

• A database can have a mixture of Oracle-managed and Oracle-unmanaged files.

  • The file system directory specified by either of these parameters must already exist; the database does not create it. 文件夹先存在
  • The directory must also have permissions for the database to create the files in it. 文件夹有权限

• In Oracle Database Cloud Service, OMF is enabled by default

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