RDM disk shows '0' byte while attaching to the virtual machine.

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• New RDM LUN or the disk reports capacity '0' B while attaching to the virtual machine while performing below task.

Navigate to Inventory>Hosts>Virtual machine then, Right-click on virtual machine and select Edit Settings.
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.

 

 

• The above Storage device which is presented to ESXi reports '0' B under Inventory>Host>Configure>Storage devices.

 

 

• Storage device reports '0' B on host UI as well and this can be checked under Host UI>Storage>Devices.

Environment

VMware vSphere ESXi 7.x

VMware vSphere ESXi 8.x

Cause

This issue caused when the operational state of the storage device shows "Detached" on ESXi host which leads to incorrect LUN size or reports '0' B.

When an RDM (Raw Device Mapping) LUN is shown as 0 bytes, it typically indicates an issue with the LUN being recognized or connected to the virtual machine. This can happen if the LUN is not properly configured, the storage array is not presenting the LUN correctly, or if there are issues with the RDM mapping itself

Virtual machine RDM disks are showing "0MB" in settings

 

Storage device status shows "Detached" under Inventory>Host>Configure>Storage devices.

 

Resolution

1. Attach the storage device to ESXi host followed by Cluster level storage rescan post which the exact LUN size reflects on the ESXi host.

• Reattach a storage device that was previously detached from the ESXi host Attach Storage Devices
• To perform cluster level storage rescan Performing a rescan of the storage on an ESXi host

2. Once the correct LUN size gets reflected on ESXi host then you proceed with configuring the RDM disk on virtual machine.

Add an RDM Disk to a Virtual Machine