vSAN Stretched Cluster (SC) provides business continuity in multiple failure situations like Fault Domains. Data is written simultaneously to two separate locations, the first location is called Preferred and the second one is called Secondary. If one of the locations is lost, the virtual machines restarts at the second location by using VMware HA, where all fresh data exists.

Before accepting this page as a reference, I strongly suggest you to review the article I wrote about SPBM again. You can  find the page here.