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Read vs Write in Quorum

I did not understand this completely: (Quorum)

  • R=1 and W=N ⇒ full replication (write-all, read-one): undesirable when servers can be unavailable because writes are not guaranteed to complete.

N = nodes in the quorum group
W = minimum write nodes
R = minimum read nodes

Writes are not guaranteed, because all N should commit and even 1 is down then it will not commit and complete a transaction.
BUT, if we read from 1 node, what happens if that node is down. This looks a more dangerous situation as it becomes ‘unavailable’.

Would you elaborate? How can we read from a node which is down?

If the data is written on all nodes, we can read from any live node.

Hello, I have a similar question about this part,

  • (N=3, W=1, R=3): fast write, slow read, not very durable
    why is read slow and write fast in this case? Shouldn’t more read nodes mean faster to read?
    Thanks.

Reading from three nodes would be slower as compared to reading from one node. Reading from three means we have to wait for all the three nodes to return data before responding to the client.

I feel the definition of N/W/R deserve bit more explanation

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