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Minimun VM witness requested

  • 30 August 2021
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Hi

I would like to know which is the minimun VM witness that I need for an specific scenario with several sites and 2-node cluster on each site.

 

At the following article I see this:

You can register multiple (different) Metro cluster pairs to a single Witness VM. One Witness VM can support up to 100 instances, that is the combined total number of protection domains in the registered Metro cluster pairs and the number of registered two-node clusters. (A single Witness VM can support both metro availability and two-node clusters.)

https://portal.nutanix.com/page/documents/details?targetId=Prism-Element-Data-Protection-Guide-v5_18:sto-metro-availability-witness-c.html

 

However at the following post I see this:

 

You can register multiple (different) Metro cluster pairs to a single Witness VM. One Witness VM can support up to 50 Witnessed Metro protection domains distributed among its registered Metro cluster pairs.

https://next.nutanix.com/installation-configuration-23/metro-availability-witness-option-38374

 

I’m a bit confused. Does it mean that if I have 70 sites with one 2-node cluster on each site, I need 2 VM witness? or would it be fine if I have 1 VM witness?

 

Thanks 

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Best answer by Nupur.Sakhalkar 31 August 2021, 23:19

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@daniel.martinez-42326 There are differences in the details mentioned in the above two links because the next community link (https://next.nutanix.com/installation-configuration-23/metro-availability-witness-option-38374) is for an older AOS version. For newer AOS releases (AOS 5.15.x and above), One Witness VM can support up to 100 instances, that is the combined total number of protection domains in the registered Metro cluster pairs and the number of registered two-node clusters. (A single Witness VM can support both metro availability and two-node clusters.) Since the portal link shared by you is for AOS 5.18, hence it states about this limit in it.

So if your AOS version is 5.15.x or above, then in this case, a single Witness VM can support up to 100 instances - this value is the combined total number of protection domains in the registered Metro cluster pairs and the number of registered two-node clusters. 

If the total number of 2-node clusters is 70, then you can use a single Witness VM for it assuming that you don’t have any Metro cluster pairs as well in your environment. 

If you have Metro cluster pairs in your environment as well in addition to the 70 2-node clusters, then the value of total number of protection domains you have on these Metro cluster pairs will determine how many Witness VMs will be needed in your case. If it is more than 30, then you will need 2 Witness VM since the total number of protection domains in the registered Metro cluster pairs and the number of registered two-node clusters will go above 100 in this case. 

Refer to the Metro Availability Witness Option section in the Data Protection Guide (latest version) on Nutanix Support Portal for more details on this one. 

 

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Thanks for the detailed explanation! :relaxed: