vSAN Stretched cluster introduced in vSAN 6.1 and it brings high availability in an active-active fashion. In this architecture, ESXi hosts would be placed in two different physical locations and join together with high bandwidth low latency networking. But from a management perspective despite hosts being in two different sites they belong to one single vSAN Cluster and share their resources. So this solution can be used in environments where disaster avoidance is a critical matter. Because it gives you the ability to avoid disaster, or recover from a disaster by having two different physical sites that host your applications. So you need to group the hosts based on their physical locations and put them in two different fault domains.
vSAN Streched Cluster Use Cases
- Plan a maintenance in one site without having any down time
- Service outage
- Unplanned outage
vSAN Stretched Cluster Requirements
Network Requirements
- Bandwidth between Data sites has to be at least 10Gbitps and the latency has to be less than or equal to (≤ 5ms ) RTT
- Network links between Data sites can be layer 2 or layer3.
- Network link between Data sites and the Witness site needs to layer 3
To know more about vSAN Stretched cluster network requirements you can check vSAN Stretched Cluster Bandwidth Sizing.
Nodes must be evenly spread between two sites
Witness node
The witness node holds the witness components and it could be installed as a dedicated physical ESXi host or a specialized virtual witness appliance. The main reason for having a witness as a virtual appliance is it does not require an extra vSphere license. To know how to deploy Witness vSAN you can read my VMware vSAN 7.0 Witness Appliance Deployment article.
MTU
For performance purposes, set the MTU to 9000 if it’s feasible in your infrastructure. But, keep it in your mind that you need to change the MTU (End-to-End)
To see how to configure vSAN Stretched Cluster in action, you can check my video on the vElements.net YouTube channel.