question

As a general rule when you want to place nodes in Cassandra racks, you should have the same number of racks as the replication factor. This is to make sure that data distribution is balanced. Otherwise, a single-rack configuration is sufficient for most environments.

The recommendation in production environments is to have 3 replicas in each DC so you need to have 3 racks. If this is not possible, you should revert your configuration to just one rack for the whole DC.

To do this, you will need to:

1. Decommission the node.
2. Completely delete all the contents (including subdirectories) of data/, commitlog/ and saved_caches/.
3. Update the node's rack configuration.
4. Add the node back to the cluster.

As a side note, this statement is incorrect:

Overload problems usually occur when performing continuous write operations that last a long time.

If the commitlog/ disk can sustain 15K IOPS, it doesn't matter if you are continuously writing to it for hours, days or months as long as you're writing at or below 15K IOPS. But if you go beyond 15K IOPS even for 1 second then you will see write failures. Cheers!