Enabling incremental backups
When incremental backups are enabled (disabled by default), Cassandra hard-links each flushed SSTable to a backups directory under the keyspace data directory. This allows storing backups offsite without transferring entire snapshots. Also, incremental backups combine with snapshots to provide a dependable, up-to-date backup mechanism.
As with snapshots, Cassandra does not automatically clear incremental backup files. DataStax recommends setting up a process to clear incremental backup hard-links each time a new snapshot is created.