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vSohill
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SAN Stretched Cluster

Hi,

If I have vSAN SAN Stretched Cluster with 4 nodes per site. If 1  Host failed on Site A and still 3 Hosts up what will happen to the VMS that runs on that host? I will configure soft and hard affinity rules.

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admin
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Hi vSohill‌,

Greetings!

Complete Site is considered as a Fault Domain in a vSAN Stretched Cluster. This means, the VMs will continue to run on the same Site till the time the complete site is not down. When complete site is down, then VMs will be restarted on another site. HA is required if you want your VMs to be restarted automatically in case of a Host Failure on a Site or a complete Site Failure.


Affinity Rules are required to make sure that HA follows those rules while restarting VMs on the same site or across sites. You need to configure Affinity Rules in such a way that Site-A VMs are grouped with Site-A hosts and Site-B VMs are grouped with Site-B hosts. You should always configure Soft Rules. (More info on Page 43-44 of http://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/products/vsan/vmware-virtual-san-6....‌)


Let me try to explain it with your scenario:

Site_A : 4 Hosts (1st Fault Domain)

Site_B : 4 Hosts (2nd Fault Domain)


Failure Scenario - Site_A with 1 Host Failure i.e 3 Hosts are up.

Result - VMs which were running on the failed host will be restarted on on the other 3 hosts automatically provided the HA is enabled on the cluster. If HA is not enabled, you have to manually restart the VMs on the other 3 Hosts.

Hope this answers your query. Smiley Happy

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Cheers!

-Shivam

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GreatWhiteTec
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You don't need to set affinity rules. There is a preferred site and a secondary site. The Failure behavior depends if the VMs on that host were either using resources, storage, or both. If those VMs were only consuming compute resources from the failed node, then HA will kick in, assuming you have that enabled. If the VM was consuming storage, then the VM(s) will be restarted on the secondary site and read storage from there. Read locality is a little different on stretched-cluster, where it reads 100% from the preferred site, and moves to 100% from secondary in case of failure/maintenance.

Check this guide for detailed behaviors on different failures. Storage and Availability Technical Documents

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admin
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Hi vSohill‌,

Greetings!

Complete Site is considered as a Fault Domain in a vSAN Stretched Cluster. This means, the VMs will continue to run on the same Site till the time the complete site is not down. When complete site is down, then VMs will be restarted on another site. HA is required if you want your VMs to be restarted automatically in case of a Host Failure on a Site or a complete Site Failure.


Affinity Rules are required to make sure that HA follows those rules while restarting VMs on the same site or across sites. You need to configure Affinity Rules in such a way that Site-A VMs are grouped with Site-A hosts and Site-B VMs are grouped with Site-B hosts. You should always configure Soft Rules. (More info on Page 43-44 of http://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/products/vsan/vmware-virtual-san-6....‌)


Let me try to explain it with your scenario:

Site_A : 4 Hosts (1st Fault Domain)

Site_B : 4 Hosts (2nd Fault Domain)


Failure Scenario - Site_A with 1 Host Failure i.e 3 Hosts are up.

Result - VMs which were running on the failed host will be restarted on on the other 3 hosts automatically provided the HA is enabled on the cluster. If HA is not enabled, you have to manually restart the VMs on the other 3 Hosts.

Hope this answers your query. Smiley Happy

_________________________

Was your question answered correctly? If so, please remember to mark your question as "Correct" or "Helpful" when you get the correct answer. This helps others searching for a similar issue.


Cheers!

-Shivam

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