Repair, or replace-address?
A dead node is not automatically a replace. The choice depends on how long it has been down, whether its data is still worth keeping, and what the rest of the ring is doing.
What to check when the cluster is already in trouble.
Short notes from production incidents. Each one is a decision you can make on a live ring: what the error actually means, which node to test, and what not to run.
ReadFailure: INDEX_NOT_AVAILABLE
An indexed query failed because a replica could not serve its storage-attached index. Test each node at LOCAL_ONE, then rebuild the index only where it failed.
Tombstones overwhelming a read
The table is up. The query scanned deletion markers until Cassandra warned or failed. Bound the read, then compact only the table the log named.