The figure below shows the topology used in this deployment. Stretched clusters require three fault domains: preferred, secondary, and witness. They may also be referred to as Sites 1, 2, and 3.
![](/static/media/9198938f-8c47-5a0e-82d9-6db6a62cd3f7/DAM-00d299c6-1de8-42dd-a436-c8d46fba1993/out/SFS with VxRail multisite stretched cluster=GUID-C4ADA9BF-CCFE-4A66-97E4-45D05FDD27FD=1=en-us=Low.png)
This design requires a SmartFabric deployed at Sites 1 and 2. Using a SmartFabric at Site 3 is optional and is not used in this example. This example uses a four-leaf/two-spine SmartFabric in Site 1, and a two-leaf SmartFabric in Site 2. At a minimum, a two-leaf SmartFabric is required at Sites 1 and 2. Up to 16 leaf switches and four spine switches are supported at each site.
When spines are used, SFS uses BGP-EVPN to stretch L2 networks across the L3 leaf-spine fabric. In a multisite topology, the L2 networks are also stretched between Sites 1 and 2 in the same manner using SFS multisite fabric interconnects.
VxRail nodes in the VxRail vSAN stretched cluster are in Sites 1 and 2. The nodes are named vxrail-01 through vxrail-06 in this example. The required witness host, named witness01, is deployed in Site 3. For this deployment example, a VMware ESXi host, named esx-svcs01, is also installed in Site 1. This ESXi host is the host for the OpenManage Network Integration (OMNI) VM and is also the initial host for a DNS and NTP services VM.