Which of the following applications used with the virtual machine would require the RDM to be in Physical Comp

A virtual machine is using a Fibre Channel attached Raw Device Mapped (RDM) LUN. Which of the following applications used with the virtual machine would require the RDM to be in Physical Compatibility Mode (Choose Three)?

A.
SAN Management Agents

B.
Physical Server to Virtual Machine Clustering

C.
Storage Array based Replication

D.
VMware Snapshots

E.
SCSI-target based software

Explanation:
Setup for Failover Clustering and Microsoft Cluster Service ESX ESXi vCenter Server, page 25.

Cluster Physical and Virtual Machines

A standby host cluster has specific hardware and software requirements. Use RDMs in physical compatibility mode (pass-through RDM). You cannot use virtual disks or RDMs in virtual compatibility mode (non-pass-through RDM) for shared storage. [B is correct].

Physical compatibility mode allows the guest operating system to access the hardware directly. Physical compatibility is useful if you are using SAN-aware applications in the virtual machine. However, a virtual machine with the physical compatibility RDM cannot be cloned, made into a template, or migrated if the migration involves copying the disk. Virtual compatibility allows the RDM to behave as if it were a virtual disk, so you can use such features as snapshotting, cloning, and so on. [Therefore D is incorrect].

Recommended Detailed Material on RDM’s
Physical mode for the RDM specifies minimal SCSI virtualization of the mapped device, allowing the greatest flexibility for SAN management software. In physical mode, the VMkernel passes all SCSI commands to the device, with one exception: the REPORT LUNs command is virtualized, so that the VMkernel can isolate the LUN for the owning virtual machine. Otherwise, all physical characteristics of the underlying hardware are exposed. Physical mode is useful to run SAN management agents [B above] or other SCSI target based software [E above] in the virtual machine.

3 Comments on “Which of the following applications used with the virtual machine would require the RDM to be in Physical Comp

  1. anitha says:

    Yes correct

    In physical mode, the VMkernel passes all SCSI commands to the device, with one exception: the REPORT LUNs command is virtualized so that the VMkernel can isolate the LUN to the owning virtual machine. Otherwise, all physical characteristics of the underlying hardware are exposed. Physical mode is useful to run SAN management agents or other SCSI target-based software in the virtual machine. Physical mode also allows virtual-to-physical clustering for cost-effective high availability.

    http://pubs.vmware.com/vsphere-50/index.jsp?topic=/com.vmware.vsphere.vm_admin.doc_50/GUID-4C0F4D73-82F2-4B81-8AA7-1DD752A8A5AC.html

  2. Anitha says:

    Please correct !

    Answer should be A , C and E

    If you use an array based solution , physical compatibility RDM’s are often used for storage of virtual machines

    See :Array based(third party) solution under vsphere storage -> overview of using ESXi with a SAN -> Layered applications

    option B is defintely incorrect because – physical compatiblity mode supports VIRTUALto physical clustering and not physical to virtual .

    1. Basil says:

      Cluster Physical and Virtual Machines
      You can create an MSCS cluster in which each physical machine has a corresponding virtual machine. This
      type of configuration is known as a standby host cluster.
      A standby host cluster has specific hardware and software requirements.

      – Use RDMs in physical compatibility mode (pass-through RDM). You cannot use virtual disks or RDMs
      in virtual compatibility mode (non-pass-through RDM) for shared storage.


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