Block-level backup (BLIB): full vs incremental

Article:HOWTO44444  |  Created: 2011-03-15  |  Updated: 2012-02-13  |  Article URL http://www.symantec.com/docs/HOWTO44444
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Block-level backup (BLIB): full vs incremental

This topic applies to policy configuration for NetBackup for VMware.

When you enable Perform block level incremental backup in the policy, NetBackup uses VMware's Changed Block Tracking feature to reduce the backup size. Since this option works at the block level (not at the file level), it applies only to backups of the entire virtual machine. It cannot be used when the policy backup selections list specifies individual files.

This option reduces the size of full backups as well as the size of incremental backups, as follows.

Table: Block-level backup of the virtual machine: full vs incremental schedule

Type of backup

Optimization that is used in backup

Backup of entire virtual machine, with full schedule

Backs up only the blocks that have changed since the .vmdk was created.

Note that uninitialized blocks are excluded from the backup.

Backup of entire virtual machine, with incremental schedule

Backs up only the blocks that have changed since the last backup, as follows:

  • For cumulative incrementals, BLIB backs up only the blocks that changed since the last full backup.

  • For differential incrementals, BLIB backs up only the blocks that changed since the previous backup of any kind.

    Note: On incremental backups, the Enable block-level incremental backup option backs up the changed files as well as their metadata.

See About reducing the size of VMware backups


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