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A customer needs a datastore to be seen across multiple vSphere clusters with applications inside of the virtual machines that must detect the physical characteristics of the storage device.
Which type of virtual disk meets this requirement?
A. A virtual disk on a VMFS datastore
B. A raw device mapped disk in virtual compatibility mode
C. A raw device mapped disk in physical compatibility mode
D. A virtual disk on an NFS datastore
Correct Answer: C
Explanation/Reference:
Explanation:
Raw device mapping (RDM) provides a mechanism for a virtual machine to have direct access to a LUN on the physical storage subsystem (Fibre Channel or iSCSI only).
You can use RDMs in virtual compatibility or physical compatibility modes. Virtual mode specifies full virtualization of the mapped device. Physical mode specifies minimal SCSI virtualization of the mapped device, allowing the greatest flexibility for SAN management software.
RDM is a mapping file in a separate VMFS volume that acts as a proxy for a raw physical storage device. The RDM allows a virtual machine to directly access and use the storage device. The RDM contains metadata for managing and redirecting disk access to the physical device.
The file gives you some of the advantages of direct access to a physical device while keeping some advantages of a virtual disk in VMFS. As a result, it merges VMFS manageability with raw device access.
RDMs can be described in terms such as mapping a raw device into a datastore, mapping a system LUN, or mapping a disk file to a physical disk volume. All these terms refer to RDMs.
Incorrect Answers:
A: VMs cannot detect the physical characteristics of the storage device when using a virtual disk. Therefore, this answer is incorrect.
B: The raw device mapped (RDM) disk needs to be in physical compatibility mode, not virtual compatibility mode for the VMs to detect the physical characteristics of the storage device. Therefore, this answer is incorrect.
D: VMs cannot detect the physical characteristics of the storage device when using a virtual disk. Therefore, this answer is incorrect.
References:
https://pubs.vmware.com/vsphere-4-esx-vcenter/index.jsp#raw_device_mapping/c_about_raw_device_mapping.html