[jng]

Nitro "virtual NVME" device are mostly (only?) for EBS -- remote network storage, transparently managed, using a separate network backbone, and presented to the host as a regular local NVME device. SSD drives in instances such as i4i, etc. are physically attached in a different way -- but physically, unlike EBS, they are ephemeral and the content becomes unavaiable as you stop the instance, and when you restart, you get a new "blank slate". Their performance is 1 order of magnitude faster than standard-level EBS, and the cost structure is completely different (and many orders of magnitude more affordable than EBS volumes configured to have comparable I/O performance).

[rcarmo]

This is the way Azure temporary volumes work as well. They are scrubbed off the hardware once the VM that accesses them is dead. Everything else is over the network.