9 Replies Latest reply on May 11, 2018 2:10 AM by Daniele_S

    VSAN Stretched Cluster & 2 Node Guide - Failure Scenario Question

    rleon_vm Novice

      Hi all,

       

      On page 138 of the following VSAN Stretched Cluster & 2 Node Guide:

      https://storagehub.vmware.com/export_to_pdf/vsan-stretched-cluster-2-node-guide

       

      ... It gives you a scenario where:

      PFTT=1, SFTT=2, FTM=R5/6

      Note: FTM is actually RAID6 in this case, because SFTT=2.

       

      So, at minimum, we have a 6+6+1 Stretched Cluster, because RAID6 requires at least 6 hosts each at the two sites. (+1 witness at a 3rd location).

       

      In one of othe failure scenarios (page 139), it says:

      Single site failure (PFTT) and single disk, disk group, host failure across remaining sites (SFTT)

      Translate: One site is down (let's say the Preferred site, doesn't matter), and in the surviving site, a single disk/diskgroup/host failure.

      Outcome: VMs gets HA restarted at the surviving site.

      The above looks right.

       

      But in another scenario (page 140), it says:

      Single site failure (PFTT) and dual disk, disk group, host failure across remaining sites (SFTT).

      This time, it says the whole cluster will be offline, all all VMs still stop running at both sites.

      My question is, isn't SFTT=2 supposed to allow two host failures in the surviving site? Why does the whole site go offline?

       

      Thanks for your input.