title: Shards and replicas in Elasticsearch
body: <p>I am trying to understand what shard and replica is in Elasticsearch, but I didn't manage to understand it. If I download Elasticsearch and run the script, then from what I know I have started a cluster with a single node. Now this node (my PC) have 5 shards (?) and some replicas (?). </p>
  
  <p>What are they, do I have 5 duplicates of the index? If so why? I could need some explanation.</p>