We have a 9 node Cassandra (V3.11) cluster and we want to add another 10 nodes to this cluster. Can we add all the 10 nodes to the cluster at the same time (with auto bootstrap parameter set to false)? And to balance the data to the newly added nodes, should we run repair or rebuild command? And can we run them on multiple machines at the same time?

Each of the existing nodes in the cluster has around 14TB disk space and out of which 11TB is already used. When we tried to add a new node, it was able to get around 5TB is around 5 days and after that the speed reduced considerably (to 200GB per day). Instead of adding one at a time, can we add all together and rebalance the data by any command?

Any pointers will be highly appreciated!

Cheers

-Siva