If the backup host or scale-out server has no track log for the given policy, bucket and query, NetBackup performs a full backup and creates a track log. The track log contains information about the objects/blobs data which is backed up as per query criteria, for comparison at the next backup.

At the next backup, NetBackup identifies data and/or metadata that has changed since the previous backup. To do so, it compares information from the track log against information from the Cloud object store for each object/blob as per the query criteria for the bucket.

The NetBackup backup host or scale-out server sends the following stream to the media server: The object/blobs' changed blocks, and the previous backup ID and data extents (block offset and size) of the unchanged blocks.

The media server receives the object/blobs' changed blocks and the backup ID and data extents of the unchanged blocks. From the backup ID and object/blob descriptors, the media server locates the rest of the object/blob's data in existing backups.

The media server directs the storage server to write the changed blocks, and combine these blocks with the locally stored, previously unchanged blocks to make a new full image."