Instance Store, EBS, and EFS

AWS Basics · Storage on AWS – EBS, Instance Store, EFS, and S3 · Lesson 3 of 5

Three storage models

Instance Store resides on the EC2 host and offers very low-latency I/O, but it is ephemeral: data is lost on stop, hibernation, termination, or host failure. Use it only for caches, buffers, and reproducible scratch data, or for software that replicates data itself across nodes.

flowchart LR
  IS["Instance Store<br/>local NVMe, ephemeral"] --> E1["EC2 in AZ 1a"]
  EBS["EBS volume<br/>zonal block"] --> E1
  EFS["EFS file system<br/>regional NFS"] --> MT1["Mount target<br/>AZ 1a, TCP 2049"]
  EFS --> MT2["Mount target<br/>AZ 1b"]
  MT1 --> E1
  MT2 --> E2["EC2 in AZ 1b"]
  %% step IS: Instance store disks are physically on the host; fastest, but data disappears when the instance moves or stops.
  %% step EBS: An EBS volume is network storage for one instance in one AZ (except io2 Multi-Attach).
  %% step EFS: EFS is one shared file system for the whole Region.
  %% step MT1: Each AZ gets a mount target with an IP in your subnet; its SG must allow NFS on 2049.
  %% step MT2: Instances mount the target in their own AZ.
  %% step E2: Many instances in different AZs read and write the same files at once.

Comparing them

	Instance Store	EBS	EFS	S3
Type	Block, local	Block, network	File (NFS v4)	Object (HTTP API)
Scope	One host	One AZ	Region (or One Zone)	Region
Shared by many instances	No	No (io2 Multi-Attach aside)	Yes, thousands	Yes, via API
Survives stop	No	Yes	Yes	Yes
Billing	Included in instance price	Provisioned GB	GB actually stored	GB stored + requests
OS	Any	Any	Linux (NFS clients)	Any, via SDK/CLI

For Windows file shares, use Amazon FSx for Windows File Server instead of EFS.

EFS details

EBS is a zonal block device, commonly serving one instance. EFS is managed regional NFS for Linux clients, with mount targets in AZs and one filesystem shared by many instances. It grows and shrinks automatically; you never provision size.

Storage classes: Standard, Infrequent Access and Archive; lifecycle management moves files not read for a set number of days to the cheaper classes.
Throughput modes: Elastic (default, scales with demand, pay per use), Provisioned (fixed MiB/s), Bursting (scales with stored size).
Performance modes: General Purpose fits latency-sensitive work; Max I/O is a legacy mode for high parallelism with higher latency.
Security: encryption at rest with KMS, TLS in transit with the mount helper's tls option, access points that force a user and root directory per application.

An EFS mount often fails when the mount-target Security Group lacks inbound TCP 2049 from the client Security Group. Install amazon-efs-utils to get the efs mount type and helper.

Instance store use cases

Temporary data that can be rebuilt: build caches, video transcoding scratch space, the buffer of a distributed database like Cassandra that keeps replicas on other nodes. Never the only copy of anything.

Command	Purpose
`aws efs create-file-system --encrypted --tags Key=Name,Value=shared`	Create an EFS file system
`aws efs create-mount-target --file-system-id fs-0a1b2c3d --subnet-id subnet-0a1b2c3d --security-groups sg-0a1b2c3d`	Add a mount target in a subnet
`sudo mount -t efs -o tls fs-0a1b2c3d:/ /mnt/efs`	Mount EFS with TLS
`df -h -t nfs4`	Verify the mount

Traps: storing the only copy of data on instance store; forgetting port 2049 in the mount target's SG; choosing EFS for Windows servers.