Think of your laptop's SSD: it stores your operating system, your files, and your applications. When you open a file, the drive responds in milliseconds. Now imagine that same drive — but physically located in a data center rack, connected to your server over a dedicated high-speed network cable. That is the mental model for EBS (Elastic Block Store).
Network Attached Storage
EBS is Network Attached Storage (NAS). The volume does not live inside your EC2 instance — it lives on dedicated storage hardware in the same AWS data center, connected over a private, high-bandwidth network that AWS calls the Nitro network. From the operating system's perspective, it looks and behaves exactly like a locally attached disk. You can format it, partition it, and run a database on it. The network is invisible.
This separation creates three important properties:
- Persistence: Your data survives EC2 instance termination. Stop the instance, detach the volume, reattach it to a different server — the data is intact.
- Flexibility: You can resize a volume, change its type, or increase its performance while it is still attached and in use (with some caveats).
- Durability: AWS automatically replicates your data across multiple physical drives within the same Availability Zone (AZ) to protect against hardware failure. If one drive dies, your data is safe.
The AZ boundary is critical: an EBS volume in us-east-1a cannot be directly attached to an EC2 instance in us-east-1b. They are physically separate facilities. Snapshots (covered later) are how you move data across AZs.
The Use Case
EBS is designed for workloads that require frequent, granular, low-latency reads and writes — the kind of access pattern where you update individual rows in a database table thousands of times per second. This is fundamentally different from object storage like S3, which is optimized for large, infrequent reads and writes of whole files.
Use EBS for:
- Operating System boot drives — every EC2 instance has a root EBS volume by default.
- Relational databases — PostgreSQL, MySQL, Oracle, SQL Server.
- NoSQL databases — Cassandra, MongoDB.
- Enterprise applications — SAP, Oracle E-Business Suite.
Do not use EBS for static assets, media files, or data shared across many servers simultaneously — that is what S3 and EFS are for.