6.0

Add an RDM Disk to a Virtual Machine in the vSphere Client
You can store virtual machine data directly on a SAN LUN instead of storing it in a virtual disk file. This
ability is useful if you are running applications in your virtual machines that must detect the physical
characteristics of the storage device. Mapping a SAN LUN allows you to use existing SAN commands to
manage storage for the disk.
When you map a LUN to a VMFS volume, vCenter Server creates a Raw Device Mapping (RDM) file that
points to the raw LUN. Encapsulating disk information in a file allows vCenter Server to lock the LUN so
that only one virtual machine can write to it at a time. For details about RDM, see the vSphere Storage
documentation.
The RDM file has a .vmdk extension, but the file contains only disk information that describes the mapping
to the LUN on the ESXi host. The actual data is stored on the LUN.
You can create the RDM as an initial disk for a new virtual machine or add it to an existing virtual machine.
When you create the RDM, you specify the LUN to be mapped and the datastore on which to put the RDM.
NOTE You cannot deploy a virtual machine from a template and store its data on a LUN. You can only store
its data in a virtual disk file.
Procedure
1 On the Select a Disk page of the New Virtual Machine wizard, select Raw Device Mapping and click
Next.
2 From the list of SAN disks or LUNs, select a LUN for your virtual machine to access directly and click
Next.
3 Select a datastore for the LUN mapping file and click Next.
You can place the RDM file on the same datastore where your virtual machine configuration file
resides, or select a different datastore.
NOTE To use vMotion for virtual machines with enabled NPIV, make sure that the RDM files of the
virtual machines are located on the same datastore. You cannot perform Storage vMotion or vMotion
between datastores when NPIV is enabled.
4 Select a compatibility mode and click Next.
Option Description
Physical
Allows the guest operating system to access the hardware directly.
Physical compatibility is useful if you are using SAN-aware applications
on the virtual machine. However, a virtual machine with a physical
compatibility RDM cannot be cloned, made into a template, or migrated if
the migration involves copying the disk.
Virtual
Allows the RDM to behave as if it were a virtual disk, so you can use such
features as taking a snapshot, cloning, and so on. When you clone the disk
or make a template from it, the contents of the LUN are copied into
a .vmdk virtual disk file. When you migrate a virtual compatibility mode
RDM, you can migrate the mapping file or copy the contents of the LUN
into a virtual disk.
5 Accept the default or select a different virtual device node.
In most cases, you can accept the default device node. For a hard disk, a nondefault device node is
useful to control the boot order or to have different SCSI controller types. For example, you might want
to boot from an LSI Logic controller and share a data disk with another virtual machine using a
BusLogic controller with bus sharing turned on.
Chapter 10 Creating a Virtual Machine in the vSphere Client
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