# Data sync issues in ES 2 nodes Master Master Cluster Set Up if one node is down

**URL:** <https://discuss.elastic.co/t/data-sync-issues-in-es-2-nodes-master-master-cluster-set-up-if-one-node-is-down/91604>\
**Category:** Elasticsearch\
**Created:** [July 3, 2017, 8:00am UTC](https://discuss.elastic.co/t/data-sync-issues-in-es-2-nodes-master-master-cluster-set-up-if-one-node-is-down/91604 "2017-07-03T08:00:29Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Priyanka\_Talwaria](https://avatars.discourse-cdn.com/v4/letter/p/439d5e/32.png) [@Priyanka\_Talwaria](https://discuss.elastic.co/u/Priyanka_Talwaria)\
**Post date:** [July 3, 2017, 8:00am UTC](https://discuss.elastic.co/t/data-sync-issues-in-es-2-nodes-master-master-cluster-set-up-if-one-node-is-down/91604/1 "2017-07-03T08:00:29Z")

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In ES-2 nodes cluster set up (Master- Master).If one node is down and meanwhile some new data is indexed on other node,then how data will be synced on both nodes when both are up?

Config Settings:

ES Config:

Node 1:

[cluster.name](http://cluster.name): mycluster  
[node.name](http://node.name): "node1"  
node.master: true  
node.data: true  
discovery.zen.ping.unicast.hosts: ["192.168.100.103"] # IP of node2  
Node 2:

[cluster.name](http://cluster.name): mycluster  
[node.name](http://node.name): "node2"  
node.master: true  
node.data: true  
discovery.zen.ping.unicast.hosts: ["192.168.101.103"] #IP of node1

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<div class="post-metadata">

**Author:** ![Christian\_Dahlqvist](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/christian_dahlqvist/32/4617_2.png) [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)\
**Post date:** [July 3, 2017, 8:15am UTC](https://discuss.elastic.co/t/data-sync-issues-in-es-2-nodes-master-master-cluster-set-up-if-one-node-is-down/91604/2 "2017-07-03T08:15:38Z")

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If you have 2 master eligible nodes in the cluster `discovery.zen.minimum_master_nodes` should be set to 2. This will stop data from being indexed while only one master eligible node is available, which will prevent data loss. If you want to be able to continue indexing while one master eligible node is unavailable, you need to have a total of 3 master eligible nodes in the cluster as this will allow the remaining 2 nodes to elect a master node by majority decision.

With your current configuration you could end up with a split brain which could lead to data loss.

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 31, 2017, 8:15am UTC](https://discuss.elastic.co/t/data-sync-issues-in-es-2-nodes-master-master-cluster-set-up-if-one-node-is-down/91604/3 "2017-07-31T08:15:46Z")

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