EBS Overview (Elastic Block Store)
What is EBS?
An EBS Volume is a network drive you attach to EC2 instances while they run. It persists data even after instance termination.
Think of EBS as a network USB stick — you can detach it from one computer and attach it to another, but through the network.
Key Characteristics
| Feature | Details |
|---|---|
| Type | Network drive (not physical) |
| Persistence | Data persists after instance termination |
| AZ Lock | Bound to specific AZ |
| Attachment | One instance at a time (CCP level) |
| Latency | Slight network latency |
| Provisioning | Must provision size (GB) and IOPS in advance |
| Billing | Billed for provisioned capacity |
| Free Tier | 30 GB/month of GP2/GP3 or Magnetic |
Architecture
┌──────────────────────────────────────────────────────────┐
│ us-east-1a │
│ │
│ ┌──────────┐ ┌──────────┐ │
│ │ EC2 │◀───▶│ EBS Vol │ 8 GB gp2 │
│ │ Instance │ │ (root) │ │
│ │ A │ └──────────┘ │
│ │ │◀───▶┌──────────┐ │
│ └──────────┘ │ EBS Vol │ 100 GB gp3 │
│ │ (data) │ │
│ └──────────┘ │
│ │
│ ┌──────────┐ ┌──────────┐ │
│ │ EC2 │◀───▶│ EBS Vol │ 8 GB gp2 │
│ │ Instance │ └──────────┘ │
│ │ B │ │
│ └──────────┘ ┌──────────┐ │
│ │ EBS Vol │ Unattached (available) │
│ └──────────┘ │
└──────────────────────────────────────────────────────────┘
- One instance can have multiple EBS volumes
- EBS volumes can be left unattached
- Cannot attach across AZs (use snapshots to move)
EBS volumes inside an AZ
Delete on Termination
| Volume | Default | Behavior |
|---|---|---|
| Root volume | Yes (enabled) | Deleted when instance terminates |
| Additional volumes | No (disabled) | Preserved after termination |
To preserve the root volume after termination, disable Delete on Termination for the root volume during launch.
Launch Instance → Storage → Advanced
└── Delete on termination: Yes / No
├── Root volume: Yes (default) → change to No to preserve
└── Additional: No (default) → data survives termination
Delete on Termination defaults
Hands-On Key Steps
- View attached volumes: Instance → Storage tab → Block devices
- Create new volume: Volumes → Create Volume → select same AZ
- Attach: Actions → Attach Volume → select instance
- Cannot attach cross-AZ (different AZ = error, no instances shown)
- Terminate instance → root volume deleted, additional volumes preserved
Questions & Answers
Q1: What is an EBS volume?
Answer:
An EBS (Elastic Block Store) volume is a network drive that you attach to EC2 instances. It provides persistent block storage that survives instance termination. Think of it as a network USB stick.
Q2: Can you attach an EBS volume to an instance in a different AZ?
Answer:
No. EBS volumes are locked to a specific AZ. To move data across AZs, you must create a snapshot and restore it in the target AZ.
Q3: What happens to EBS volumes when you terminate an EC2 instance?
Answer:
- Root volume: Deleted by default (Delete on Termination = Yes)
- Additional volumes: Preserved by default (Delete on Termination = No)
You can change this behavior during instance launch.
Q4: Can an EC2 instance have multiple EBS volumes?
Answer:
Yes. You can attach multiple EBS volumes to a single instance, like plugging multiple USB sticks into one computer. Each volume can have different sizes and types.
Q5: Can an EBS volume exist without being attached to an instance?
Answer:
Yes. EBS volumes can be created and left unattached (status: "available"). They can be attached on demand to any instance in the same AZ.
Q6: Why is there latency with EBS volumes?
Answer:
Because EBS is a network drive, not a physical drive. Communication between the instance and the volume goes over the network, introducing some latency compared to directly attached storage.
Q7: How is EBS billing calculated?
Answer:
You're billed for provisioned capacity (size in GB and IOPS), not actual usage. You can increase capacity over time. Free tier includes 30 GB/month of GP2/GP3 or Magnetic.
Q8: How do you preserve the root volume after instance termination?
Answer:
During instance launch, go to Storage → Advanced and set Delete on Termination to "No" for the root volume. This prevents the root EBS from being deleted when the instance terminates.
Q9: Can you attach one EBS volume to multiple instances simultaneously?
Answer:
At the basic level, no — one EBS volume attaches to one instance at a time. However, io1/io2 volumes support Multi-Attach (up to 16 instances in the same AZ), covered in the EBS Volume Types section.
Q10: What is the EBS free tier?
Answer:
30 GB per month of free EBS storage of type General Purpose (SSD) or Magnetic. This is available for the first 12 months of an AWS account.
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