RF2 -> RF3 | Requirements

  • 5 March 2020
  • 3 replies
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Giving thought to change your replication factor from 2 to 3? What are the impacts and things to consider?

 

First, let’s take a look at what replication factor is. Redundancy factor is a configurable option that allows a Nutanix cluster to withstand the failure of nodes or drives in different blocks.

 

By default, Nutanix clusters have redundancy factor 2, which means they can tolerate the failure of a single node or drive. 

So RF3 means cluster can tolerate the failure of 2 nodes or drive… Basic Maths isn’t it?

 

Redundancy factor 3 has the following requirements:

  1. Redundancy factor 3 can be enabled at the time of cluster creation or after creation too.

  2. A cluster must have at least five nodes for redundancy factor 3 to be enabled.

  3. For guest VMs to tolerate the simultaneous failure of two nodes or drives in different blocks, the data must be stored on containers with replication factor 3.

  4. Controller VMs must be configured with a minimum of 28 GB(20 GB default+8 GB for the feature) of memory.

 

To take a look at the CVM memory configuration requirements for cluster features and add-ins, take a look at:-

https://portal.nutanix.com/page/documents/details/?targetId=Advanced-Admin-AOS-v5_16:app-cvm-memory-config-feats-r.html

 

To know how to increase the Replication factor, take a look at the document:- https://portal.nutanix.com/#/page/docs/details?targetId=Web-Console-Guide-Prism-v5_16:wc-cluster-fault-tolerance-update-ui-t.html

 

To know more about Redundancy Factor 3, take a look at the document:-

https://portal.nutanix.com/#/page/docs/details?targetId=Web-Console-Guide-Prism-v5_16:arc-redundancy-factor3-c.html


3 replies

Interestingly, the NCP test exam disagrees here.

 

It claims that:

  • 24GB is not a requirement for the CVMs
  • A cluster can be converted from RF2 to RF3

 

Userlevel 4
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Hey @jchristiaens-35502,

I hope you are doing good and are healthy. Thanks for pointing out. I have corrected the point 1 and modified point 4 with the correct number. Also provided a link to check the CVM memory config for cluster features.

 

Thanks and Regards,

Shaurya

Is there a way to preview what the change from RF2 to RF3 as you suggest will impact the overall cluster resources? If you have a CVM already configured with more ram, will it require an additional 8 to accommodate the feature?

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