> For the complete documentation index, see [llms.txt](https://ysfang82.gitbook.io/development-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ysfang82.gitbook.io/development-notes/aws-notes/service/storage/efs.md).

# EFS

**Introduction**

* Elastic File System (EFS) is a file storage service for EC2. Connecting to EFS is similar to connecting to your network drive.
* EFS is within your VPC. Create each ENI (mount target) per AZ.
* The capacity is elastic, can grow / shrink automatically.
* 3x expensive than EBS, 20x expensive than S3.

**Feature**

* **Compatible for Linux**, POSIX-compliant.
* Supports the Network File System version 4 (NFSv4) protocol
* Scaling:
  * 1000s of concurrent NFS connections, 10 GB +/s throughput
  * Grow to Petabyte-scale
* Performance mode (According to how data is consumed. Set at EFS creation time):
  * General purpose (default): latency-sensitive use cases
  * Max I/O: higher latency / throughput, parallel processing (big data, media processing)
* Throughput mode (To determine the Bandwidth):
  * Bursting mode (scales as the size grows): common for file systems
  * Provisioned IO mode: high throughput to storage ratio (if burst is not enough, more expensive)
* Storage tiers (lifecycle management: move file after N days)
  * Standard: for frequently accessed file
  * Infrequent access: higher cost to retrieve the file, lower price point to store the file.
* Use 2 Security Groups for EFS / EC2 communications.
  * Create an inbound / outbound rule to allow the NFS port (TCP:2049) for the EFS mount target / EC2.
* Encryption at rest with KMS.
  * Encryption at rest has to be enabled when the file system is created. 
* Encryption in transit
  * Enable TLS when mounting the EFS by adding the `-o tls` option such as: `sudo mount -t efs -o tls fs-12345678:/ /mnt/efs`.
* Read after write consistency
* Working with on-prem servers, better to have a Direct Connect for security and high performance
  * Otherwise, suggest to use Amazon [DataSync](https://aws.amazon.com/datasync/?whats-new-cards.sort-by=item.additionalFields.postDateTime\&whats-new-cards.sort-order=desc) to connect EFS and on-prem servers.

**Scenario**

* VPC Peering & EFS on-premise
  * Setup VPC peering for another VPC to access the EFS.
  * Setup Direct Connect / site-to-site VPN that supports IPSec for on-premise server to access the EFS by IPv4 (not DNS).