Final answer:
EFS, or Amazon Elastic File System, uses the NFS protocol for file-level storage, with support for versions 4.0 and 4.1. It allows EC2 instances to simultaneously access data and is scalable and elastic, integrating with AWS services.
Step-by-step explanation:
The protocol used by EFS, which stands for the Amazon Elastic File System, is the Network File System (NFS) protocol. EFS is a file storage service for use with Amazon Web Services (AWS) and it is designed to be scalable, elastic, and to provide easy integration with other AWS services. Unlike SMB (Server Message Block) which is primarily used for Windows-based systems, or EBS (Elastic Block Store), which provides block-level storage volumes for use with EC2 instances, EFS provides file-level storage and uses NFS, specifically versions 4.0 and 4.1, allowing multiple EC2 instances to access the file system simultaneously. Other protocols mentioned, like HTTP, are not used by EFS for file storage, as they serve different purposes like web content delivery.