# Catch up of a new read-replica or a core server does not work

**URL:** <https://community.neo4j.com/t/catch-up-of-a-new-read-replica-or-a-core-server-does-not-work/18950>\
**Category:** Neo4j Graph Platform\
**Tags:** cluster\
**Created:** [May 20, 2020, 9:48am UTC](https://community.neo4j.com/t/catch-up-of-a-new-read-replica-or-a-core-server-does-not-work/18950 "2020-05-20T09:48:58Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![michalkomorowski1984](https://sea1.discourse-cdn.com/flex021/user_avatar/community.neo4j.com/michalkomorowski1984/32/8476_2.png) [@michalkomorowski1984](https://community.neo4j.com/u/michalkomorowski1984)\
**Post date:** [May 20, 2020, 9:48am UTC](https://community.neo4j.com/t/catch-up-of-a-new-read-replica-or-a-core-server-does-not-work/18950/1 "2020-05-20T09:48:58Z")

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According to my understanding when a new read-replica or a new core server is added to a healthy cluster they should start synchronization. This behaviour is described here:

- [Causal Clustering lifecycle - Operations Manual](https://neo4j.com/docs/operations-manual/3.5/clustering-advanced/lifecycle/#causal-clustering-lifecycle-core-membership)
- [Causal Clustering lifecycle - Operations Manual](https://neo4j.com/docs/operations-manual/3.5/clustering-advanced/lifecycle/#causal-clustering-catchup-protocol)

Now we are trying to add a new core server (or a replica) to a cluster but with no-downtime. Initially, we tried to add an empty node to a cluster but it didn't catch up. So now we are trying to restore a database from a backup and then try to add a node to a cluster. However, we observed that if there are any changes e.g. only adding 10 nodes then a new core server or a new replica cannot catch up with a cluster even after 30 minutes.

Do you have any idea what may be wrong?