Underlying S3 bits do bite you when you deal with lots of small files. Our team even considered maintaining NFS or Gluster servers over horrible EFS performance.
Another file system that works well with lots of small files and that doesn't require maintaining any extra servers is ObjectiveFS[0]. It is a FUSE based log structured file system (with snapshots) using GCS or S3 for log storage with memory cache and (optional) disk cache for performance.
