When creating a VMFS datastore the iSCSI service must be running on the TrueNAS, and a portal must be created. Otherwise this action will fail in vCenter. I am unsure if this is a bug or something we need to document around. My instinct tells me that we should provide an option for the user to select the portal, and create the first portal if none exist. I would say check with Kris, Dru to determine how this should behave for our initial version.