They likely were running data on EBS volumes instead of bare metal SSDs, due to ease of recovery (a failed instance does not lose data on the attached EBS volum

They likely were running data on EBS volumes instead of bare metal SSDs, due to ease of recovery (a failed instance does not lose data on the attached EBS volumes). You can only run your DBs on bare metal SSDs if you are prepared to lose a node’s data completely. In fact, many instance types no longer have any ephemeral storage attached and it’s a default practice to use EBS for root and data volumes. There are some instance types that have extremely fast EBS performance (EBS io2 Block Express), which has hardware acceleration and an optimized network protocol for EBS network I/O and offers sub-millisecond latency. However, these are expensive and get even more so if you go up in IOPS.