WAC Wizard 3 Node switchless

Question

Hi together,

can the wac (2103.2) wizard create a 3 node switchless /full mesh cluster or only with a physical switch? (with 20h2)

best regards

Daniel

Answer 1

Hi @Daniel Fabian ,

For a 3-node, switchless HCI cluster, you would need two storage NICs per node (a single 2-port NIC like you have also works for this). The reason for this is because each node would need to connect to the other two nodes of the cluster directly. This is in addition to at least one other NIC that would be used for management and VM traffic (could be more). It is also HIGHLY recommended to put these two storage NICs onto separate subnets/VLANs due to the way SMB multichannel establishes connections over the storage networks. If you put both ports on the same subnet, SMB multichannel will assume each host should be able to connect to all storage NICs on both hosts and will attempt to do so. However, because it will only be able to connect to the directly-attached NIC, you will see some errors in the event logs as the cross-connection attempts would fail.

Also, we don't recommend using APIPA addresses for the storage adapters. As the traffic going across those storage adapters won't be routable, you could assign pretty much any address to those adapters just so long as they don't conflict with an actual address on your local network. Another reason APIPA is not recommended is because these address will change at reboot, so it may take a bit longer to rediscover the endpoint. Finally, an APIPA address is used by the cluster adapter once it comes online (by-design), so you want to avoid having any subnet overlap there as well.

That said, I tested this configuration and attempted to create a cluster via Windows Admin Center. I too received the same error that you noted above, and WAC would not allow me to proceed with testing. I did attempt to put all of the addresses on the same two subnets just to see what would happen. What I found was that WAC failed the connectivity tests (as expected). If I were to click on the 'Details' next to the failure, it showed me that the ping between the non-directly connected NICs was what failed. However, it did allow me at this point to continue with the cluster creation if I wanted.

Unfortunately, WAC doesn't cover every possible scenario for how clusters could be configured. For this scenario, it seems it would currently be better suited to build the cluster via PowerShell initially. This way, you can configure the optimized addressing scheme keeping each interconnect on its own subnet. Once the cluster is built, you could then manage the cluster via Windows Admin Center without issue.

Hope this helps!
Trent

Answer 2

Hi Daniel, I believe it should be fine, as long as WAC can reach all 3 nodes on the NICs attached to your management network.

Please let us know if you run into issues.

Thanks!
Matt

Answer 3

Hi Matt,

thank you for your response.

we try a single nic (25Gb 2p 640FLR) configuration for the rdma network. (Management network is OK) but the assistant can't handle it.

Ping test with apipa addresses in the same subnet fails. that is clear

If we divide it into subnets we get the message:

"Error Check the IP addresses and subnet masks — for servers to talk to each other, every server should have the same number of adapters within each subnet."

sounds like we need another nic in every server.

ping test in powershell from each host works with ip´s and subnets over the mesh network.

Thanks
Daniel

Answer 4

Hi Trent,

thank you very much

good to know.

we build the cluster with powershell

Daniel