EBS (Elastic Block Store)
AZ-scoped storage (tied to one AZ)
Can move across AZ/region using snapshots
Block storage (like a disk)
Attached to EC2 → needs filesystem (ext4/xfs)
Multi-Attach
Only io1/io2
Same AZ only
Max 16 instances
Supports concurrent read/write
❗ Requires cluster-aware filesystem (AWS doesn’t handle locking)
EFS (Elastic File System)
Regional service (multi-AZ by default)
File storage (NFS)
Can be mounted to 100s of EC2 instances at the same time
Linux only
Auto-scaling (capacity planning available via provisioned option)
Higher cost than EBS
Lifecycle policies used to move data to cheaper tier based on Last accessed.
Instance Store (Ephemeral Storage)
Physically attached storage to EC2 instance
Provides very low latency and high IOPS
Ephemeral (temporary storage)
Data behavior:
Lost on instance STOP or TERMINATION
NOT lost on reboot
Key characteristics:
No persistence
No snapshots or backup
Not detachable or reusable
Use cases:
Caching (Redis, Memcached)
Temporary / scratch data
Buffer storage
HPC intermediate processing
Key decision rule:
Use Instance Store when data can be LOST
Use EBS when data MUST persist
One Liner
Single instance → EBS
Multi-instance, same AZ → Multi-Attach EBS
Multi-instance, cross-AZ → EFS
Shared file system without management → EFS
EBS => One server mindset
EFS = Shared storage mindset
Instance storage Highest I/O performance among EC2-attached storage
No network overhead (physically attached)
Very low latency
