Time to scale Cassandra cluster again, I think 10 is 1 reasonable number. I also want to do 1-year test, for that we expect 24TB of data for 3 replicas, with some overhead 3TB per server node is probably OK. But it may be interesting to look at dynamics after 1 year (if we don't run out of money), so 4TB per node is probably better. I think local SSDs come in multiples of 4, 8*375GiB = 3000GiB, 12*375GiB = 4500GiB. I don't think it's possible to attach more disks without stopping instance which destroys the data, so we need to plan capacity ahead.