Howdy folks. I asked some about this in IRC yesterday, but we're looking to hopefully confirm a couple of things for our sanity.
Yesterday, I was performing an operation on a 21-node cluster (vnodes, replication factor 3, NetworkTopologyStrategy, and the nodes are balanced across 3 AZs on AWS EC2). The plan was to swap each node's existing 1TB volume (where all cassandra data, including the commitlog, is stored) with a 2TB volume. The plan for each node (one at a time) was basically: - rsync while the node is live (repeated until there were only minor differences from new data) - stop cassandra on the node - rsync again - replace the old volume with the new - start cassandra However, there was a bug in the rsync command. Instead of copying the contents of /var/data/cassandra to /var/data/cassandra_new, it copied it to /var/data/cassandra_new/cassandra. So, when cassandra was started after the volume swap, there was some behavior that was similar to bootstrapping a new node (data started streaming in from other nodes). But there was also some behavior that was similar to a node replacement (nodetool status showed the same IP address, but a different host ID). This happened with 3 nodes (one from each AZ). The nodes had received 1.4GB, 1.2GB, and 0.6GB of data (whereas the normal load for a node is around 500-600GB). The cluster was in this state for about 2 hours, at which point cassandra was stopped on them. Later, I moved the data from the original volumes back into place (so, should be the original state before the operation) and started cassandra back up. Finally, the questions. We've accepted the potential loss of new data within the two hours, but our primary concern now is what was happening with the bootstrapping nodes. Would they have taken on the token ranges of the original nodes or acted like new nodes and got new token ranges? If the latter, is it possible that any data moved from the healthy nodes to the "new" nodes or would restarting them with the original data (and repairing) put the cluster's token ranges back into a normal state? Hopefully that was all clear. Thanks in advance for any info!
