vSAN Disks Are SSD Disks – Showing as HDD Inside Guest OS

Products

• VMware vSAN

Issue/Introduction

In a vSAN environment, virtual disks backed by SSD devices are displayed as HDD inside the guest operating system.

Example Observation (Guest OS):

Powershell showing media type as HDD

PS C:\Windows\system32> Get-PhysicalDisk | Select-Object DeviceID, MediaType, Size, SerialNumber

DeviceID     MediaType                  Size       SerialNumber 

1                  HDD            107######304      6000##########################2c

0                  HDD            106######160      6000##########################77

Example Observation (vSAN / ESXi):

less localcli_vsan-storage-list.txt | grep -i ssd
   Is SSD: true
   Is SSD: true
   Is SSD: true
   Is SSD: true
   Is SSD: true

less localcli_storage-core-device-list.txt | grep -i ssd
   Is SSD: true
   Is SSD: true
   Is SSD: true
   Is SSD: true
   Is SSD: true
   Is SSD: true

From the vSAN and ESXi perspective, all physical devices are SSD, but inside the VM, the disk appears as HDD.

Example (WMIC and PowerShell outputs):

The WMIC outputs show:

C:\Users\Administrator>wmic diskdrive get model, mediatype

MediaType : HDD
Model      : VMware Virtual disk SCSI Disk Device

Powershell:

PS C:\Users\Administrator> Get-PhysicalDisk | Format-Table FriendlyName, MediaType, BusType

FriendlyName           MediaType        BusType

VMware Virtual disk     HDD                  SAS

This confirms that the guest OS identifies the virtual disk as HDD, even though the backing datastore is SSD-based vSAN storage.

Environment

• VMware vSAN 8.x
• VMware vSAN 7.x

Cause

• The parameter scsiX:Y.virtualSSD (where X is the SCSI controller number and Y is the virtual disk number) is not set in the VM’s configuration file (.vmx).
• By default, VMware presents all virtual disks as HDDs unless explicitly configured otherwise.
• VMware abstracts physical storage and presents virtual devices to the guest OS. The virtualSSD parameter acts as a metadata flag instructing the hypervisor to advertise the virtual disk as SSD. When this flag is missing or set to FALSE, the hypervisor reports the virtual disk to the guest OS as HDD - regardless of whether the backing storage is SSD, NVMe, or vSAN.
• Additionally, vSAN does not pass low-level SSD information directly to the guest OS. Since vSAN is a software-defined storage (SDS) solution that aggregates local storage devices (SSD/HDD) into a shared datastore, VMs consume storage from this logical datastore, not from physical disks directly.

Resolution

To make the guest operating system recognize the virtual disk as SSD:

1. Power off the virtual machine.

2. Navigate to VM --> Edit Settings --> VM Options --> Advanced --> Configuration Parameters.

3. Click Add Configuration Parameter and add the following entry:

   scsi0:0.virtualSSD = "TRUE"

   (Adjust the controller and disk number according to your configuration.)

4. Power on the virtual machine.

5. Verify inside the guest OS using:

   Get-PhysicalDisk | Select-Object DeviceID, MediaType

   The disk should now show MediaType = SSD.

Additional Information

• This configuration change only affects how the guest OS perceives the virtual disk type.

• It does not alter performance because the actual performance characteristics are determined by the underlying datastore (vSAN or SSD-backed storage).

• Some guest-level features (e.g., Windows Storage Spaces tiering, deduplication, defragmentation policies) rely on the disk being recognized as SSD for optimal functionality.