Various methods, systems, and processes for mitigating fragmentation in synthetic full backups are disclosed. One or more storage units out of multiple storage units are identified. The multiple storage units include one or more new storage units or one or more existing storage units. The multiple storage units are accessed and a determination is made as to whether the one or more storage units out of the multiple storage units meet a threshold. The threshold is a measure of a characteristic of those one or more storage units. If one or more storage units meet the threshold, those one or more storage units are included in a backup stream, and the backup stream is sent to a backup server.