Deleting snapshot files
When taking a snapshot, previous snapshot files are not automatically deleted. You should remove old snapshots that are no longer needed.
The nodetool clearsnapshot command removes all existing snapshot files from the snapshot directory of each keyspace. You should make it part of your back-up process to clear old snapshots before taking a new one.
$ nodetool -h localhost -p 7199 clearsnapshot
To delete snapshots on all nodes at once, run the nodetool clearsnapshot command using a parallel ssh utility.