Host does not recognize its devices as flash even though the disks are SSD/Flash.

Products

• VMware vSphere ESXi

Issue/Introduction

This article provides steps to mark the device as Flash, if VMware does not recognize SSDs as flash disk.

ESXi does not recognize certain devices as flash when their vendors do not support automatic flash disk detection. The Drive Type column for the devices shows HDD as their type.

Environment

7.x
8.x

Cause

ESXi does not recognize certain devices as flash when their vendors do not support automatic flash disk detection. The Drive Type column for the devices shows HDD as their type.

Resolution

Prerequisites:

Verify that the device is not in use and make sure that you have SSD disks on backend storage.

 

Procedure:

1. In the vSphere Client, navigate to the ESXi host.
2. Click the Configure tab.
3. Under Storage, click Storage Devices.
4. From the list of storage devices, select one or several HDD devices and click the Mark as Flash Disk.
5. Click Yes to save your changes.

Note: If the flash device that you mark is shared among multiple hosts, make sure that you mark the device from all hosts that share the device.

Additional Information

When you mark a disk as flash disk, VMware primarily tries to use it as a cache for the datastore. Since SSDs are much much faster than hard disks it improves the performance of the datastore. If you mark a hard disk as flash disks VMware tries to use it as a cache, expecting very low seek times and high throughput.

 

Impact/Risks:

Marking the HDD devices as flash might deteriorate the performance of datastores and services that use them. Mark the devices only if you are certain that they are flash devices.