Add new RDM to existing Microsoft Windows Server Failover Clustering (WSFC) VMs
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Add new RDM to existing Microsoft Windows Server Failover Clustering (WSFC) VMs

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Article ID: 391820

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Updated On: 03-30-2025

Products

VMware vSphere ESXi

Issue/Introduction

This article explains the process of adding new pRDM to an existing set of Windows Server Failover Clustering (WSFC) VMs.

Environment

VMware vSphere ESXi 7.x

VMware vSphere ESXi 8.x

Resolution

Below are the steps for this activity:

  1. First perform the below on the primary node:
    1. Right click on VM in vSphere Client and select "Edit Settings".
    2. On the Virtual Hardware tab, click the "Add New Device" button and select "RDM Disk" from the drop-down menu. The Select Target LUN dialog box opens.
    3. In the Select Target LUN dialog box, select the target LUN for the raw device mapping and click OK. The disk appears in the virtual device list.
    4. Select the location for the mapping file.
      • To store the mapping file with the virtual machine configuration file, select Store with the virtual machine.
      • To select a location for the mapping file, select Browse and select the datastore location for the disk.
    5. Select the compatibility mode - Physical.
    6. Select sharing as "no sharing".
    7. Select the required controller and thus the "virtual device node".
    8. Step 1.7 needs to be made a note of as the same RDM should be added with the same "virtual device node" value on the other VMs sharing this pRDM.
    9. Click "OK" to save the configuration.
  2. Next, perform the below on the additional nodes:
    1. Right click on VM in vSphere Client and select "Edit Settings".
    2. On the Virtual Hardware tab, click the "Add New Device" button and select "Existing disk" and then browse to the same datastore and folder where the added RDM's pointer file (.vmdk) is stored and select it.
    3. This will add the RDM to this VM as well.
    4. Select the required configuration for the disk, and then set the "virtual device node" as that what was noted in step 1.7.
    5. Click "OK" to save the configuration.
  3. Step 1 and 2 will be performed for each new pRDM which is to be added to the clustering VMs.

Additional Information

Is downtime for the VMs required to perform this activity?

  • Downtime will not be required to add the RDMs to the VMs.
  • But it is recommended to perform the activity during off business hours as hot changes to virtual machine hardware might disrupt the heartbeat between the WSFC nodes. This can cause the cluster services to failover.
  • Hot add disk or hot share disk is supported.
  • So if a potential failover of the services is not desired to occur due to loss in heartbeat then the activity can be performed after taking a downtime.
  • A shared disk resource provided by pRDM can be extended online or offline.

 

Microsoft Windows Server Failover Clustering (WSFC) with shared disks on VMware vSphere 8.x: Guidelines for supported configurations

Microsoft Windows Server Failover Clustering (WSFC) with shared disks on VMware vSphere 7.x: Guidelines for supported configurations