This article originally started off life as a record of how I managed to get this working, as a lot of my posts do, but this time it appears I am foiled. Last week, I had 3 vCenter Servers that appeared to be happily talking to each other in Linked Mode sharing a singe Multi-site SSO domain without any real issues. I had a single-pane-of-glass view of all 3 and I could manage them all from the one client.
VMware vSphere Single Sign On (SSO) can be installed in Multi-site mode to support local sign-on to vCenters that you want to be part of the same single sign on domain - for example, if you want to install Linked-Mode and have the advantage of a single pane of glass view, but can’t risk using a single SSO instance across the WAN. In other words, from VMware’s blog post: Multisite deployments are where a local replica is maintained at remote sites of the primary vCenter Single Sign-On instance.