topic vSAN across WAN in VMware vSAN Discussions

vSAN across WAN

zeebahi — Wed, 09 Dec 2020 01:11:51 GMT

Hi everybody,

I am trying to find if there is any maximum network latency limit for vSAN.

We have to sites in two different continents, the round trip time between the two is 230msec. We are wondering if we can still do vSAN with cluster stretched between these two locations.

Thanks and have a good night!!

Re: vSAN across WAN

daphnissov — Wed, 09 Dec 2020 01:15:20 GMT

Yeah that's not going to work at all. vSAN does have a max latency requirement and that's way too far.

Re: vSAN across WAN

zeebahi — Wed, 09 Dec 2020 01:25:25 GMT

Thanks !!!

I just found out:

Network latency

Maximum of 1 ms RTT for standard (non-stretched) vSAN clusters between all hosts in the cluster
Maximum of 5 ms RTT between the two main sites for stretched clusters
Maximum of 200 ms RTT from a main site to the vSAN witness host

Re: vSAN across WAN

depping — Wed, 09 Dec 2020 07:42:48 GMT

No, this is not possible. This would severely hurt your application performance, to the point where you will have all users of the application shouting at you. If you want to increase availability, consider using async replication and SRM for orchestration. This will provide you the ability to failover VMs after a failure between the locations.

Keep in mind, a Stretched Cluster means ALL writes need to be acknowledged by BOTH locations before they are acknowledged to the VM, in other words, every write IO will take 200+ MS. I am sure that would not be acceptable in terms of performance.