How the NetBackup Accelerator works
The NetBackup Accelerator creates the backup stream and backup image as follows:
If the client has no previous backup, NetBackup performs a full backup and creates a track log. The track log contains information about the client's data, for comparison at the next backup.
At the next backup, NetBackup identifies data that has changed since the previous backup. To do so, it compares information from the track log against information from the file system for each file. For NTFS and ReFS file systems, it also uses the Windows change journal to help identify the data that has changed since the last backup.
Accelerator uses the Windows change journal in two ways: To check for changes in the file system metadata, and to help detect which files have changed since the last backup.
The NetBackup client sends to the media server a backup stream that consists of the following: The client's changed blocks, and the previous backup ID and data extents (block offset and size) of the unchanged blocks.
The media server receives the client's changed blocks and the backup ID and data extents of the unchanged blocks. From the backup ID and file system descriptors, the media server locates the rest of the client's data in existing backups.
The media server directs the storage server to write the changed blocks and the unchanged blocks in a new full image.
Figure: NetBackup client: Accelerator backup stream shows how an Accelerator backup stream is composed.
Figure: NetBackup media server constructs backup image shows how the media server constructs a backup image from the Accelerator stream and from previous backups:
Figure: Process overview of Accelerator backup recaps Accelerator details in the context of the principal NetBackup processes.
