> So if I understand correctly, the nodes getting the replica copies are > predetermined, based on the replication strategy.
Yes, pre-determined as a function of ring layout (which nodes have which tokens), the replication factor, and the replication strategy. > One thing is still a bit unclear. So once a node establishes who its > replicants are, are those "replicant nodes" always used? To be clear, it's not that there is a primary node that internally decides who is responsible for data. Rather, given the known rules for determining which nodes are responsible for a given row key, any node in the cluster is aware of that information. In order to satisfy consistency levels during read and write operations, requests are routed as appropriate to nodes that are responsible for the row key. So yes, the nodes responsible for a given row key are always used for reads and writes to that row key. > In other words, given a RF=3, if the other two replica nodes go down, the > "original" node will not automatically pick 2 new nodes for its replica > copies? No. Actually moving data between nodes is done by ring management operations; i.e., an operator deciding to decommission or move nodes. Moving data is quite an expensive/significant operation and there is no automatic mechanism to do this. The way to survive nodes going down is to select an appropriate replication factor on the key space, and select an appropriate consistency level for reads and writes. (The only exception would be hinted hand-off when writing at CL.ANY and hinted hand-off, but I'll leave that beyond the scope of this.) -- / Peter Schuller
