Virtualised MSCS (VMWare)

This relates to vSphere 5.5

Below vSphere 6 MSCS isn’t supported as a guest but even with vS6 it’s only supported with RDMs (Raw Device Mappings).

However you can build a cluster providing you remember the following rules:

  • You CANNOT use vMotion
    • this will create duplicate blanks of the shared disks
    • recovering from this requires deleting the duplicates and then manually re adding the shared disks from within the Virtual Machine configuration
  • the boot and cluster disks MUST be on different SCSI controllers
    • The scsi controller must be ParaVirtual
    • the shared disks MUST be thick provisioned (eager zeroed thick)
  • The cluster validation tool will always show warnings about disk and network but as long as the ERROR messages are cleared it will work
  • Resizing a cluster shared disk reverts it to lazy zeroed thick and you have to ‘eager’ it from the ESX cli as it’s not possible via the GUI.
    • From the correct foler in the correct datastore run
      • vmkfstools –eagerzero nameofvmdk.vmdk
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Windows Server Failover Clusters – Removing Mount Point Disks

Really why, in all that is within the realms of common sense, does MS CS default to removing all disk resources from a group if you do not offline the resource beforehand?

Surely just blocking the option would be easier?

The technet article is not the first that appears when you research removing disks from a cluster or even the second  or third or fourth (you have to search on removing disks from the group) … although it may now be moving it up the search ratings.

The crux of the article is:

“Now, we get to the main point of this post. The above process is fine for deleting resources from a cluster group unless the resource you are deleting is configured as a “Physical Disk’ resource, and it a mount point disk. The process differs slightly and you must follow this process or you could find yourself unintentionally moving every resource in the group into ‘Available Storage’.”

Yes the online storage is linked to the cluster, yes the cluster will fail if an online resource is removed, but why remove all the mountpoints from the group rather than just denying the action!

And there’s an added gotcha, occasionally it will not just move the disks out of the group, it will online them on the other cluster node. Which leaves you in the state of having the mountpoints on one node and the named disks and cluster IP(s) on the other.

In summary and to avoid that classic head meets desk moment, in order to remove a mount point volume from an MSCS group you have to:

  • offline the disk
  • remove it from the group
  • delete the resource
  • delete the SAN storage volume
  • rescan both nodes