title: Extending Cassandra cluster with datacenter in China (CGF)
body: <p>I need to extend my cluster with a new datacenter to be present in China mainland, behind the Great Firewall. Currently I have datacenters in the US and Europe - so the cluster already matches to the requirements of the <a href="https://www.datastax.com/dev/blog/multi-datacenter-replication" rel="noreferrer">Geographical Location Scenario</a>.</p>
  
  <p>At this point I have the chinese infrastructure ready for Cassandra, but the network statistics from the past few days are bit troublesome and I am a bit afraid: <strong><em>if and how this can effect my current cluster</em></strong> and will be the new datacenter functional at all?</p>
  
  <p>My actual questions regarding this are:</p>
  
  <ul>
  <li>How does Cassandra handle huge packet-loss during replication? (occasionally up to 40%)</li>
  <li>How does it effect the cluster when the network connection between two datacenters are really bad (only few kilobits/sec and latency as above) for hours?
  
  <ul>
  <li>Will the chinese dc considered as dead? Or Cassandra will still try to use the limited bandwidth? </li>
  <li>Can this cause any problem on the non-chinese datacenters? e.g. they get slow, which results in client request timeouts.</li>
  </ul></li>
  <li>Is it possible to enforce somehow, that only one of my non-chinese datacenter communicates with the chinese one? Or should I trust that Cassandra will handle this? (trying to avoid to possible harm all my datacenters)</li>
  <li>Is there any way to fasten up the initial data replication (<code>nodetool rebuild</code>), because with the current speed it would take weeks to replicate our current data.</li>
  </ul>
  
  <p>Any suggestion or remark is welcomed, thanks!</p>