Ring View

• Nodes are positioned around the ring according to their assigned token. In the case of ByteOrderedPartioner or vnodes, nodes are positioned based on what percentage of data they own.
• The color of each node represents its health, which is determined by system load average (the number shown by the uptime command). Per core: 0–0.999 is Normal (green); 1–5 is Medium (yellow); 5+ is High (red).
• The size of each node represents its data size, relative to all other nodes in the cluster.

Health summary

The health summary pane, located above the rings, contains a cluster-wide summary of the data represented within the rings. You can quickly get an idea of the health of your cluster without having to manually scan each ring. This is especially useful with larger clusters.

Hovering over a number in the health summary will highlight the nodes included in that total. You can easily identify potential problem nodes, as well as whether or not multiple nodes within a single replica set are having issues.

Clicking on the totals in the health summary presents a list of nodes included in the total.

Node details

Hovering over a node displays some basic details about that node. These details are updated in real time.

Clicking a node reveals a dialog displaying more information so you can run various operations on the node.

Streams

The progress of any streams between nodes is shown graphically within the ring.

Node positioning 

The goal of positioning nodes in a ring is to visually represent whether a datacenter is balanced or not (that is, data is more likely to be evenly distributed across nodes). In a healthy ring, nodes will be spread out evenly around the ring.

When a cluster uses RandomPartitioner or Murmur3Partitioner for its snitch, its nodes are positioned around the ring according to their assigned token, but there are some cases where positioning by token does not make sense:

• If vnodes are enabled, each node is made up of multiple virtual nodes (256 by default), so positioning by token would mean having hundreds of times as many nodes around the ring.
• If a partitioner that doesn't use consistent hashing is used, such as ByteOrderedPartitioner, data is not guaranteed to be distributed evenly, so positioning by token also has no guaranteed value

In those cases, nodes are positioned based on the percentage of data they own in the ring, so a healthy ring is still represented by nodes being evenly spaced out.

Unknown datacenter list

Rings are displayed by datacenter. This information is gathered from the agent that runs on each node. If the agent is not installed or has not connected properly, or there are any other problems getting datacenter information for a node, it is displayed in a special list above all rings.