title: Spark StorageLevel - When to use MEMORY_ONLY_2, MEMORY_AND_DISK_2 etc?
body: <p>The advantage of <code>RDD</code> is by default Resilient, it can rebuild the broken partition based on lineage graph.</p>
  
  <p>Then why do we need to use this <code>Storage Levels</code> like <code>MEMORY_ONLY_2</code>, <code>MEMORY_AND_DISK_2</code> etc, this is basically to replicate each partition on two cluster nodes.</p>