Data transfer between Elasticsearch Data Nodes

Hi Everyone,

In my deployment, I have 3 node elasticsearch cluster in kubernetes environment and 5 clients are writing data to this cluster at rate of ~7MB/s per elasticsearch data node and NO READ operation is performed. Below are the few configurations Elasticsearch configuration details. Two mount points are configured in two different disks for storing the data, also number of shards is 6 and there is no replication. What we have observed that there is ~10MB/s data transfer is happening between the elasticsearch data nodes. So, could someone please explain about this internode data transfer and is there a way to reduce it. Thanks.

iftop -B output:

metrics-datastore-0.metrics-datastore.a10harmony.svc.cluster.local   => metrics-datastore-1.metrics-datastore.a10harmony.svc.cluster.local                       12.2MB  15.4MB  14.4MB
                                                                     <=                                                                                          11.3MB  14.1MB  14.1MB
metrics-datastore-0.metrics-datastore.a10harmony.svc.cluster.local   => metrics-datastore-2.metrics-datastore.a10harmony.svc.cluster.local                       21.4MB  15.2MB  14.4MB
                                                                     <=                                                                                          21.9MB  13.9MB  13.9MB

ES Version details:

bash-4.1# curl -XGET 'localhost:9200'
{
"name" : "metrics-datastore-0",
"cluster_name" : "metrics-datastore",
"cluster_uuid" : "cNKU0p_2TVGzN350m3KXKw",
"version" : {
"number" : "6.6.0",
"build_flavor" : "default",
"build_type" : "tar",
"build_hash" : "a9861f4",
"build_date" : "2019-01-24T11:27:09.439740Z",
"build_snapshot" : false,
"lucene_version" : "7.6.0",
"minimum_wire_compatibility_version" : "5.6.0",
"minimum_index_compatibility_version" : "5.0.0"
},
"tagline" : "You Know, for Search"
}

ES settings:

index.number_of_replicas": 0,
index.number_of_shards: 6,
index.refresh_interval: 30s,
index.translog.durability: async,
index.translog.flush_threshold_size: 1g,
index.translog.sync_interval: 10s,
index.unassigned.node_left.delayed_timeout: 10m,
index.mapping.total_fields.limit: 3000

path.data: /data/elasticsearch/data,/data2/elasticsearch/data
path.logs: /logs/elasticsearch,/logs2/elasticsearch

discovery.zen.fd.ping_interval: 10s
discovery.zen.fd.ping_retries: 5
discovery.zen.fd.ping_timeout: 120s
gateway.recover_after_master_nodes: 2
gateway.recover_after_data_nodes: 2
gateway.recover_after_time: 5m
gateway.expected_data_nodes: 3
gateway.expected_master_nodes: 3
gateway.expected_nodes: 6
http.cors.enabled: false
indices.fielddata.cache.size: 10%
indices.memory.index_buffer_size: 30%
thread_pool.write.queue_size: 2000
network.bind_host: , local
network.publish_host:
logger.gateway: TRACE