If ESXi does not automatically recognize its devices as flash, mark them as flash devices.
Verify that the device is not in use.
- Browse to the host in the vSphere Web Client object navigator.
- Click the Manage tab, and click Storage.
- Click Storage Devices.
- From the list of storage devices, select one or several HDD devices that need to be recognized as flash devices and click the Mark as Flash Disks icon.
- Click Yes to save your changes.
What to do next
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.