Script: Finding RDM LUN UUIDs in a vSphere Cluster

Posted on Aug 8, 2016 Updated on Mar 13, 2026

If you’re managing a large virtual environment, keeping track of Raw Device Mappings (RDMs) can be a nightmare. Unlike standard virtual disks (VMDKs) that live neatly inside a datastore, RDMs are directly mapped to a LUN on your SAN.

When your storage team asks, “Which VM is using LUN ID 55?”, you don’t want to check every VM manually. This PowerCLI script will scan your entire cluster and export a list of all RDMs along with their Canonical Name (NAA ID) and Device Name.

The PowerCLI One-Liner

This command connects to your cluster, filters for disks that are either RawPhysical (Pass-through) or RawVirtual, and spits out the details to a text file for easy searching.

Run this in your PowerCLI window:

PowerShell

Get-Cluster 'YourClusterName' | Get-VM | Get-HardDisk -DiskType "RawPhysical","RawVirtual" | Select-Object @{N="VM";E={$_.Parent.Name}},Name,DiskType,ScsiCanonicalName,DeviceName | Format-List | Out-File –FilePath C:\temp\RDM-list.txt

Breaking Down the Output

Once you open C:\temp\RDM-list.txt, here is what you are looking at:

• Parent: The name of the Virtual Machine.
• Name: The label of the hard disk (e.g., “Hard disk 2”).
• DiskType: Confirms if it’s Physical (direct SCSI commands) or Virtual mode.
• ScsiCanonicalName: The NAA ID (e.g., naa.600601...). This is the “Universal ID” your storage array uses.
• DeviceName: The internal vSphere path to the device.

Why do you need this?

1. Storage Migrations: If you are decommissioning a storage array, you must identify every RDM to ensure you don’t leave a “Ghost LUN” behind.
2. Troubleshooting Performance: If a specific LUN is showing high latency on the SAN side, this script tells you exactly which VM is the “noisy neighbor.”
3. Audit & Compliance: Great for keeping a monthly record of physical hardware mappings.

Lazy Admin Note: This script specifically uses VMware PowerCLI cmdlets (Get-HardDisk). If you are looking for similar info on a Hyper-V host, you would typically use Get-VMHardDiskDrive and look for the DiskNumber property to correlate with physical disks in Disk Management.