DataStax Academy FAQ

DataStax Academy migrated to a new learning management system (LMS) in July 2020. We are also moving to a new Cassandra Certification process so there are changes to exam bookings, voucher system and issuing of certificates.

Check out the Academy FAQ pages for answers to your questions:


question

rashmimisal07_190319 avatar image
rashmimisal07_190319 asked ·

How many nodes can be down with replication factor of 3 and consistency LOCAL_QUORUM?

Replication-3,Consistency-Local_Quorum,Nodes-10,How many nodes

afford to go down so that application is not affected.

replication
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bettina.swynnerton avatar image
bettina.swynnerton answered ·

Hi @rashmimisal07_190319,

if you have replication factor 3 per datacenter, and you read or write with LOCAL_QUORUM, you can at maximum afford to have one node down before your application is affected.

Does this answer your question?

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Nodes-20,5 nodes can be afforded to be down, What can be the

replication factor- ?

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Erick Ramirez avatar image
Erick Ramirez answered ·

To add to Bettina's answer, I think you missed the point.

Requests with consistency level LOCAL_QUORUM with the recommended replication factor of 3 requires a quorum of 3 replicas -- with quorum being "50% + 1", that means 2 out of 3 replicas are required to satisfy the request.

As I understand it, you've passed the certification for both Administrator Associate and Developer Associate so I think you should be able to work out how many replicas you need for requests to succeed when you have 5 nodes down in a 20-node DC using the formula I provided. Cheers!

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your right that i have passed certification but i want to check my ans with you i know the formula and better know how to use it.

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Erick Ramirez avatar image Erick Ramirez ♦♦ rashmimisal07_190319 ·

Good to hear. Cheers!

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