设置

replication factor：副本因子

查看各个 KeySpace 的 rf：

SELECT * FROM system_schema.keyspaces;

修改：https://docs.datastax.com/en/cql-oss/3.3/cql/cql_using/useUpdateKeyspaceRF.html

-- 使用 NetworkTopologyStrategy
ALTER KEYSPACE system_auth WITH REPLICATION =
  {'class' : 'NetworkTopologyStrategy', 'dc1' : 3, 'dc2' : 2};
-- 使用 SimpleStrategy，并指定 rf
ALTER KEYSPACE "Excalibur" WITH REPLICATION =
  { 'class' : 'SimpleStrategy', 'replication_factor' : 3 };

Procedure

1. Update a keyspace in the cluster and change its replication strategy options.

cqlsh> ALTER KEYSPACE system_auth WITH REPLICATION =
{‘class’ : ‘NetworkTopologyStrategy’, ‘dc1’ : 3, ‘dc2’ : 2};

1. Or if using SimpleStrategy:

cqlsh> ALTER KEYSPACE “Excalibur” WITH REPLICATION =
{ ‘class’ : ‘SimpleStrategy’, ‘replication_factor’ : 3 };

1. Note: Datacenter names are case sensitive. Verify the case of the using utility, such as nodetool status.
2. On each affected node, run nodetool repair with the -full option.
3. Wait until repair completes on a node, then move to the next node.For more about replication strategy options, see Changing keyspace replication strategy
   

Repairing nodes：

https://docs.datastax.com/en/archived/cassandra/3.0/cassandra/operations/opsRepairNodesTOC.html
修复数据不一致

Read Repair：

https://docs.datastax.com/en/archived/cassandra/3.0/cassandra/operations/opsRepairNodesReadRepair.html

nodetoll repair -full