LankyDoodle-7423 avatar image
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LankyDoodle-7423 asked ·

Failover Clustering - Cluster Sets


I was just wondering about Cluster Sets. Does this overcome the requirement of having the CPUs aligned to not have to use processor compatibility for failover VMs between nodes; a lot of what I read about Cluster Sets is the ability to use hardware diversity.

Also, can you can the individual clusters be different sizes, in terms of nodes?


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MicoMi-MSFT avatar image
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MicoMi-MSFT answered ·

Please check the following docs:
Processor Compatibility Mode in Hyper-V

If you plan to move virtual machines, without rebooting them, between virtualization hosts that may use different generations of processors, you should enable processor compatibility mode. For example, you would enable processor compatibility mode to ensure that you can live migrate your virtual machines between cluster nodes that use different processor feature sets. You could also use processor compatibility mode to save a virtual machine and restore it on a host computer that has a different processor feature set than the source host.

Performance Impact of Hyper-V CPU Compatibility Mode

Planning Failover Cluster Node Sizing

So let’s say you have 1,000 VMs… if you have a single 32-node cluster, and the entire cluster goes down, that means all 1,000 VMs go down. Where if you had them broken into two 16-node clusters, then only 500 VMs (half) go down. Defining fault domains can protect you from cluster class failures.
The larger the cluster, the more nodes Dynamic Optimization has to work with and the better balancing it can achieve. So while creating multiple smaller clusters may divide up multiple fault domains, creating too small of clusters can increase the management and keep them from being utilized optimally. Defining a larger cluster creates finer granularity to spread and move across.

Thanks for your time!
Best Regards,
Mico Mi

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Hi Mico,

Thanks for your reply.

One thing I'm also struggling to get a definitive answer on is how failover works between Cluster Set Members. MS docs say one of the reasons to use Cluster Sets is if you want to Live Migrate between Clusters, however I'm also seeing docs that say failover between Cluster Sets is manual rather than automatic.

If you can Live Migrate, doesn't that suggest failover is automatic as well? Granted, I can understand the storage aspect, i.e. if using HCI, you'd ALSO need to Storage Replicate between all the Cluster Set Members.

Thanks again

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MicoMi-MSFT avatar image MicoMi-MSFT LankyDoodle-7423 ·

Kindly check this doc and may be helpful at your side:
Why is there automatic failover for HA and manual failover for DR?

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