Simplivity stretched cluster minimum omnistack nodes

[Fabiosouza-br]

Good Morning!

I have a customer who wants to make a MetroCluster to support a mini automation datacenter, he needs RPO=0 in this case.

He already has 2 Simplivity Small nodes connected to each other via 10GbE DAC and communication to the network is through 1GbE Base-T ports (picture attached), he wants to place 2 more identical nodes in another Rack and make a stretched cluster between these clusters to replicate a maximum of 15 virtual machines.

Is this possible? or do we have to put at least 3 nodes in each cluster and add 10Gb switches for that?

Thank you for your help.

[gustenar]

Hello @Fabiosouza-br 

Thank you for using HPE SimpliVity Forums. 

Here are some guidelines to use stretched clusters (From HPE SimpliVity Administration Guide):

• Existing cluster size and network guidelines apply to Stretched Clusters.

• Place the Arbiter in a third physical site.

• Additional requirements for the Stretched Clusters feature are as follows:

◦ Stretched Clusters are supported with an even number of HPE OmniStack hosts. Hosts must be equally distributed in the two Availability Zones within the cluster. Stretched Clusters are not supported with an odd number of hosts.

◦ Stretched Cluster configurations support up to 16 HPE OmniStack hosts.

The recommended max latency value between availability zones is 2ms, a 10Gbps connection is recommended. 

Here is some additional material that could be of help: 

HPE SimpliVity - Stretch Clusters - Overview 

HPE SimpliVity - Stretch Clusters - Configure 

HPE SimpliVity - Stretch Clusters - Unconfigure 

Hope it helps, 

gustenar

[Fabiosouza-br]

Thank you @gustenar

I understood that it cannot be an odd number of equipment. In other words, I cannot have at least 3 nodes in each cluster, but can I have at least 2 nodes?

I didn't find this information anywhere.

[gustenar]

Correct, you can have 2,4,6,8 nodes per availability zone. The max supported is 16 nodes. 

It has to be the same cluster though, even if they are in a separated rack. Not separate clusters. What you create are availability zones in the cluster. 

[Fabiosouza-br]

Tks @gustenar 

Last doubt, the Nodes are connected DIRECT CONNECT, can I keep it that way, or do I have to use a 10GBE switch for this?

[Ryan_Hardy]

Well, how would you direct connect 4+ hosts to each other?

Yes, you have to use 10g switches for that. I've been there: started with 2 direct connected hosts in separate rooms (= stretched), but as soon as I needed a third host, I had to use switches. What I learned after that: uneven numbers in clusters aren't cool. Especially with SimpliVity you're gonna have VMs on hosts with the VMs storage on the wrong hosts. The inbuild logic will move the data often to the wrong hosts, even if you correct it manually.

What you have in mind is way better (although more expensive): put as much hosts as needed in one site and put the same amount in another site to replicate the data there. Of course you need twice the hardware, but you can tolerate the loss of a complete datacenter site. One question remains: can you accept normal vSphere HA (watch for licensing!) or do you need FT?

Oh, and please use decent switches for storage traffic or the customer won't be happy.