How to know the synchronization is complete between data nodes in MySQL Cluster ? (no replies)

As the subject,

Now i have created a MySQL Cluster,

mgmt node *1
sql node *1
data node A (Master) *1
data node B (Slave) *1

One day i got the situation:

1. data node A crash
2. data node B being the Master data node
3. continue to writing datas to data node B
4. data node A repaired succeed & connect to MySQL Cluster

So, the question is,
how could i know data node A & B is syncing ?
how could i konw when the synchronization is complete ?

Is there any files of logs or status could be observe?