Implications of Marking HDD Devices as SSD in vSphere
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Implications of Marking HDD Devices as SSD in vSphere

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Article ID: 424896

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Updated On:

Products

VMware vCenter Server VMware vSphere ESXi

Issue/Introduction

Symptoms

A storage administrator or user requests to manually change the disk type of a local storage device from HDD to Flash (SSD) within vCenter. This is often requested to satisfy specific application requirements (e.g., a NAS Virtual Machine) or to enable features that require SSD-backed datastores.

Environment

 

  • VMware ESXi 8.x

  • VMware vCenter Server 8.x

 

Resolution

While vSphere allows you to manually "Mark as Flash" for devices that the ESXi host does not automatically recognize as SSD, this should only be done if the underlying physical hardware is actually Flash-based.

Risks of Marking HDD as SSD:

Manually marking a physical spinning disk (HDD) or a RAID group of HDDs as Flash does not change the physical performance characteristics of the drive. It can lead to the following issues:

  • Performance Deterioration: Datastores and services expect high IOPS and low latency from Flash devices. Marking an HDD as Flash can cause these services to behave poorly.

  • High Latency: If a VM (like a NAS appliance) believes it is running on SSD, it may attempt to push heavy I/O workloads. A RAID-6 HDD array cannot match these speeds, resulting in massive latency spikes that could impact all VMs residing on that host.

  • Inaccurate Reporting: Performance monitoring and capacity planning tools will report inaccurate data, as they will be measuring HDD performance against SSD benchmarks

Recommendations:

  1. Do Not Change the Type: It is strongly recommended not to mark the device as SSD if the underlying hardware is HDD.

  2. Verify Hardware: The "Mark as Flash" feature is strictly intended for cases where the hardware vendor does not support automatic detection of an actual Flash device.

Additional Information

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