索引被分解成碎片，以便分布它们和扩展它们。

副本是碎片的副本。

节点是弹性搜索的一个运行实例，属于一个集群。

集群由一个或多个具有相同集群名称的节点组成。每个集群都有一个由集群自动选择的主节点，如果当前的主节点发生故障，可以将其替换。

如果你真的不喜欢看到它变黄。您可以将副本的数量设置为0:

curl -XPUT 'localhost:9200/_settings' -d '
{
    "index" : {
        "number_of_replicas" : 0
    }
}
'

请注意，您应该只在本地开发框上执行此操作。

索引被分解成碎片，以便分布它们和扩展它们。

副本是分片的副本，在节点丢失时提供可靠性。这个数字经常会引起混淆，因为副本计数== 1意味着集群必须有可用的分片的主副本和复制副本才能处于绿色状态。

为了创建副本，您的集群中必须至少有2个节点。

你可能会发现这里的定义更容易理解: http://www.elasticsearch.org/guide/reference/glossary/

在ElasticSearch中，在顶层，我们将文档索引为索引。每个索引都有若干个分片，这些分片内部分布数据，而这些分片内部存在Lucene段，这是数据的核心存储。因此，如果索引有5个分片，这意味着数据已经分布在各个分片上，并且分片中存在不同的数据。

请观看解释ES核心的视频 https://www.youtube.com/watch?v=PpX7J-G2PEo

关于多索引或多碎片的文章 弹性搜索，多个索引vs不同数据集的一个索引和类型?

I will explain this using a real word scenarios. Imagine you are a running a ecommerce website. As you become more popular more sellers and products add to your website. You will realize the number of products you might need to index has grown and it is too large to fit in one hard disk of one node. Even if it fits in to hard disk, performing a linear search through all the documents in one machine is extremely slow. one index on one node will not take advantage of the distributed cluster configuration on which the elasticsearch works.

So elasticsearch splits the documents in the index across multiple nodes in the cluster. Each and every split of the document is called a shard. Each node carrying a shard of a document will have only a subset of the document. suppose you have 100 products and 5 shards, each shard will have 20 products. This sharding of data is what makes low latency search possible in elasticsearch. search is conducted parallel on multiple nodes. Results are aggregated and returned. However the shards doesnot provide fault tolerance. Meaning if any node containing the shard is down, the cluster health becomes yellow. Meaning some of the data is not available.

To increase the fault tolerance replicas come in to picture. By deault elastic search creates a single replica of each shard. These replicas are always created on a other node where the primary shard is not residing. So to make the system fault tolerant, you might have to increase the number of nodes in your cluster and it also depends on number of shards of your index. The general formula to calculate the number of nodes required based on replicas and shards is "number of nodes = number of shards*(number of replicas + 1)".The standard practice is to have atleast one replica for fault tolerance.

设置碎片数量是一个静态操作，这意味着您必须在创建索引时指定它。在此之后的任何改变都需要完全重新索引数据，并且需要时间。但是，副本数量的设置是一个动态操作，也可以在索引创建后的任何时间完成。

您可以使用下面的命令为索引设置碎片和副本的数量。

curl -XPUT 'localhost:9200/sampleindex?pretty' -H 'Content-Type: application/json' -d '
{
  "settings":{
    "number_of_shards":2,
    "number_of_replicas":1
  }
}'

索引被分解成碎片，以便分布它们和扩展它们。

副本是碎片的副本。

节点是弹性搜索的一个运行实例，属于一个集群。

集群由一个或多个具有相同集群名称的节点组成。每个集群都有一个由集群自动选择的主节点，如果当前的主节点发生故障，可以将其替换。