ESXi does not recognize certain devices as flash when their vendors do not support automatic flash disk detection.
Verify that the device is not in use. Ensure the virtual machine(s) accessing the device are powered off and if it contains a mounted datastore, ensure that the datastore is unmounted. For more information on the unmounting operation, see How to unmount a LUN or detach a datastore device from ESXi hosts.
Browse to the host in the vSphere Client object navigator.
Click the Configure tab.
Under Storage, click Storage Devices.
From the list of storage devices, select one or several HDD devices to mark as flash devices and click the Mark as Flash Disks icon.
Notes:
# esxcli storage nmp satp rule add --satp VMW_SATP_LOCAL --device <naa device ID>
Error adding SATP user rule: Duplicate user rule found for SATP VMW_SATP_LOCAL matching device <naa device ID> PSP and PSP Options
# esxcli storage nmp satp rule remove --satp VMW_SATP_LOCAL --device <naa device ID>
# esxcli storage nmp satp rule add --satp VMW_SATP_LOCAL --device <naa device ID> --option "enable_ssd"