ESX Configuration Guide

VMware recommends that you use virtual disk files for the cluster-in-a-box type of clustering. If you plan to reconfigure your cluster-in-a-box clusters as cluster-across-boxes clusters, use virtual mode RDMs for the cluster-in-a-box clusters.

Managing Mapped LUNs

You can use the vSphere Client to map a SAN LUN to a datastore and manage paths to your mapped LUN.

Additional tools available to manage mapped LUNs and their RDMs include the vmkfstools utility and other commands used with the vSphere CLI. You can use the vmkfstools utility to perform many of the same operations available through the vSphere Client.

You can also use common file system commands in the service console.

Create Virtual Machines with RDMs

When you give your virtual machine direct access to a raw SAN LUN, you create a mapping file (RDM) that resides on a VMFS datastore and points to the LUN. Although the mapping file has the same.vmdk extension as a regular virtual disk file, the RDM file contains only mapping information. The actual virtual disk data is stored directly 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 creating the RDM, you specify the LUN to be mapped and the datastore on which to put the RDM.

Procedure

1Follow all steps required to create a custom virtual machine.

2In the Select a Disk page, select Raw Device Mapping, and click Next.

3From the list of SAN disks or LUNs, select a raw LUN for your virtual machine to access directly.

4Select a datastore for the RDM mapping file.

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.

5Select a compatibility mode.

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, powered on virtual machines that use RDMs configured
	for physical compatibility cannot be migrated if the migration involves
	copying the disk. Such virtual machines cannot be cloned or cloned to a
	template either.
Virtual	Allows the RDM to behave as if it were a virtual disk, so you can use such
	features as snapshotting, cloning, and so on.

6Select a virtual device node.

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Chapter 10 Raw Device Mapping

7If you select Independent mode, choose one of the following.

Option	Description
Persistent	Changes are immediately and permanently written to the disk.
Nonpersistent	Changes to the disk are discarded when you power off or revert to the
	snapshot.

8Click Next.

9 In the Ready to Complete New Virtual Machine page, review your selections. 10 Click Finish to complete your virtual machine.

Manage Paths for a Mapped Raw LUN

You can manage paths for mapped raw LUNs.

Procedure

1 Log in as administrator or as the owner of the virtual machine to which the mapped disk belongs. 2 Select the virtual machine from the Inventory panel.

3On the Summary tab, click Edit Settings.

4On the Hardware tab, select Hard Disk, then click Manage Paths.

5Use the Manage Paths dialog box to enable or disable your paths, set multipathing policy, and specify the preferred path.

For information on managing paths, see “Using Multipathing with ESX,” on page 117.

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