Notes on Synthetic Backups

General Notes:

• Synthetic backups are supported on the following NetBackup 5.0 server platforms: Sun Solaris, Microsoft Windows, AIX, Hewlett-Packard, and Linux Red Hat.
• The option to create multiple copies is not allowed for synthetic backups.
• Synthetic backups are not supported if any of the component images are encrypted.
• A user-generated backup image cannot be used to generate a synthetic image.

NetBackup must be configured to use the binary catalog format:

Synthetic backups cannot be created from catalogs in ASCII format.

Catalogs converted from ASCII to binary using cat_convert will not work. Synthetic backups and the associated catalog are identical to those of non-synthetic backups, except that the image time for synthetic backups is one second after the time of the latest component image, and not the time that the synthetic backup was actually created.

Synthetic backup jobs create two sets of catalog files:

When a synthetic backup job is run, two sets of catalog files are created: an image file and one or more .f files.

1. The first set is named using the time stamp of the most recent incremental + 1. This set represents the actual synthetic backup image which is as recent as the most recent incremental.
2. The second set is named using the current time stamp. This set is used to mark the time the synthetic backup job was run. It does not contain any file data.

Do not manually remove any of these catalog files. The catalog files are automatically expired after the retention period as specified in the schedule for the policy. The two sets of catalogs have the same expiration time.

For example:

True Image Restore and Synthesized Backups

Since True Image Restore with Move Detection is required for synthetic backups, all clients included in the policy must support TIR.

The TIR information in the image catalog is normally pruned (removed) after the number of days indicated in the master server host property, Keep True Image Restoration (TIR) Information.

However, if a synthetic full and/or synthetic cumulative schedule has been defined in the policy, the TIR information will not be pruned from the component images until a subsequent traditional or synthetic full or cumulative backup image has been generated successfully.

For example, if the host property specifies that TIR information is to be pruned from the catalog after two days, on the third day the TIR information will be pruned only if a traditional or synthetic full backup image has been generated.

If the TIR information has been pruned from one or more component images and you accidentally expire the most recent synthetic image, if you try to rerun the synthetic backup job, it will automatically restore the TIR information to the catalog. In case the TIR information cannot be restored due to bad, missing, or vaulted media, the synthetic backup job will fail with error code 136 (TIR info was pruned from the image file). If the problem is correctable, you can run the synthetic backup again.

Checkpoint Restart and Synthesized Backups:

If Checkpoint Restart (Take Checkpoints setting onthe policy Attributes tab) is indicated for the policy, the backups produced with the synthetic backup schedule will not be checkpointed. Selecting Take Checkpoints for synthetic backups has no effect.

Change Journal and Synthesized Backups:

If the Change Journal host property is enabled for a client, the property will have no effect when the client is backed up using the synthetic backup schedule.