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EBS vs EFS vs Instance Store
Block vs shared file vs ephemeral storage. Pick by attachment model and durability needs.
The three you must not confuse
- EBS: network block volume attached to one instance in one AZ (persistent). Think a hard drive.
- EFS: managed NFS file system many Linux instances across AZs mount concurrently (elastic).
- Instance store: physically attached, fast, and ephemeral — gone on stop/terminate.
Key architectural decisions
- Need shared access from a fleet? EFS. Single high-IOPS DB volume? EBS io2.
- Match EBS type to need: gp3 general, io1/io2 for consistent high IOPS, st1/sc1 for throughput/cold HDD.
- EFS has lifecycle management to move cold files to IA automatically.
Gotchas & exam traps
- "Shared across many EC2 instances" => EFS, not EBS (EBS multi-attach is a narrow exception).
- Instance store data loss on stop is a classic durability trap.
- Windows shared file system => FSx, not EFS.
The architect view
Storage questions are really attachment-model questions. Decide single-attach vs shared vs throwaway first, and the service picks itself.