Note_Tech

All technological notes.

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DBA - Backup Sets and Image Copies

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• DBA - Backup Sets and Image Copies
  • Dynamic Views
  • Backup Sets
    • Command
  • Image Copies
    • Command
  • Backup Set vs Image Copy
  • Proxy copies

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Dynamic Views

• Dynamic Views about backups:

Dynamic View	Description
V$BACKUP_SET	Backup sets created
V$BACKUP_ PIECE	Backup pieces that exist
V$DATAFILE_COPY	Copies of data files on disk
V$BACKUP_ FILES	Information about all files created when creating backups

• If using recovery catalog:

View	Description
RC_BACKUP_SET	Backup sets created
RC_BACKUP_ PIECE	Backup pieces that exist
RC_DATAFILE_COPY	Copies of data files on disk
RC_BACKUP_ FILES	Information about all files created when creating backups

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Backup Sets

• backup pieces

  • a binary file contains a backup of one or more database files.

• Backup sets:

  • a collection of backup pieces
  • an RMAN-exclusive format
    • only created and accessed through RMAN
    • the only form in which RMAN can write backups to media managers such as tape drives and tape libraries.

• Characteristics:

  • can be sent
    • to the disk
    • to the tape directly.
  • empty data blocks are not stored, thereby causing backup sets to use less space on the disk or tape.
  • can be compressed to further reduce the space requirements of the backup.
  • A backup set can contain multiple data files.
    • e.g.,
      • you can back up 10 data files into a single backup set consisting of a single backup piece.
      • In this case, RMAN creates one backup piece as output. The backup set contains only this backup piece.

• Advantage:

  • better space usage, significantly reduce the space required by the backup.

• Disadvantage:

  • With backup sets, the entire backup set must be retrieved from your backup location before you extract the file or files that are needed.

• In most systems, the advantages of backup sets outweigh the advantages of image copies.

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Command

• The FORMAT parameter

  • specifies a pattern to use in creating a file name for the backup pieces created by this command.

• The FORMAT specification can also be provided through the ALLOCATE CHANNEL and CONFIGURE commands.

BACKUP AS BACKUPSET
FORMAT '/BACKUP/df_%d_%s_%p.bus'
TABLESPACE hr data;

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Image Copies

• Image copies:

  • a bit-by-bit copy of a single data file, archived redo log, or control file.

• can be created 创建方式

  • with the BACKUP AS COPY command
  • with an operating system command.

• When you create the image copy with the RMAN BACKUP AS COPY command, the server session validates the blocks in the file and records the copy information in the control file. 验证并记录在 cf 中

• Characteristics:

  • can be written only to disk.只能写到磁盘.注意该处是直接写入. image copy 可以拷贝到 tape.

    • When large files are being considered, copying may take a long time, but restoration time is reduced considerably because the copy is available on the disk. 备份时长, 但恢复时短

  • If files are stored on disk, they can be used immediately by using the SWITCH command in RMAN, which is equivalent to the ALTER DATABASE RENAME FILE SQL statement. 在磁盘上可以马上使用

  • In an image copy, all blocks are copied, whether they contain data or not, because an Oracle database process copies the file and performs additional actions such as checking for corrupt blocks and registering the copy in the control file. 复制所有块, 包括未使用的.

  • To speed up the process of copying, you can use the NOCHECKSUM parameter. By default, RMAN computes a checksum for each block backed up and stores it with the backup. When the backup is restored, the checksum is verified.作为恢复时验证项之一.默认项.
  • An image copy can be part of a full or incremental level 0 backup because a file copy always includes all blocks. You must use the level 0 option if the copy will be used in conjunction with an incremental backup set. 可以作为全备份

• Advantage:

  • improved granularity of the restore operation. With an image copy, only the file or files need to be retrieved from your backup location. 可以精准取回需要的文件.

• Disadvantage:

  • Space usage, Image copies back up every data block, even if the data block is empty.

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Command

Configuration:

CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COPY;

Backup

BACKUP AS COPY DATABASE PLUS ARCHIVELOG;
BACKUP AS COPY DATAFILE '/ORADATA/users_01_db0l.dbf';
BACKUP AS COPY ARCHIVELOG LIKE '/arch$';

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Backup Set vs Image Copy

• advantage of creating backups as image copies

  • It improves the granularity of the restore operation.
    • With an image copy, only the file or files need to be retrieved from your backup location. 仅提取必须文件
    • With backup sets, the entire backup set must be retrieved from your backup location before you extract the file or files that are needed. 整体提取.

• the advantage of creating backups as backup sets

  • It has better space usage.
    • In most databases, 20% or more of the data blocks are empty blocks.
    • Image copies back up every data block, even if the data block is empty.
    • Backup sets significantly reduce the space required by the backup.
  • In most systems, the advantages of backup sets outweigh the advantages of image copies.

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Proxy copies

• Proxy copies:
  • a feature that enables a media manager to manage completely the transfer of data between disk and backup media.
  • The media manager then determines how and when to move the data.

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• Backups may be stored as:
  • Image copies
  • Backup sets
  • Proxy copies

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