Use datacenter id

[jfriesse]

Datacenter id is already read from cmap and sent to qnetd, but afterwards it is not used. Implement support at least for fifty-fifty split, so it will possible to handle case with 2 data centers (sites) each with 2 nodes and requirement of 2 nodes must be from same data center. Or other way, cluster shouldn't be quorate if there is 1 node from datacenter A and 1 node from datacenter B.

[eeoooue]

Could you explain a bit more about why this would this be desirable? Is it a consideration of network latency?
For a stretch cluster with 2 of 4 nodes online and an active QDevice, I would have thought we would want to maintain quorum regardless of where the available nodes are physically located.

[jfriesse]

Hi, just to clarify, such feature (if implemented) would be optional. And you are right, main reasoning is latency, but not really for corosync/qdevice itself, but rather for shared disk. The specific use case was AFAICR customer having 2 datacenters, each datacenter is having it's 2 nodes and own iscsi disk. And redundancy is required inside datacenter, so basically, when datacenters split, one is fenced-out, but problem might happen if datacenter connection is ok but for some reason each datacenter looses one node. Honestly, I'm still unsure if this is really task for qdevice, and if such configuration should really be one cluster instead of having two clusters (so geo clustering), but as we all know, The customer is always right.