Amazon EBS: Elastic Block Store

Amazon Elastic Block Store (EBS) provides persistent block-level storage volumes for EC2 instances. If S3 is like a warehouse of objects, EBS is like a hard drive attached to your server — fast, low-latency, and designed for workloads that need frequent read/write operations.

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What Is Block Storage?

Block storage divides data into fixed-size chunks called blocks. Each block has an address, and the operating system can read and write individual blocks directly. This is how traditional hard drives and SSDs work.

Characteristic	Block Storage (EBS)	Object Storage (S3)
Data model	Fixed-size blocks	Complete objects (file + metadata)
Access	Mounted as a volume	HTTP API
Latency	Sub-millisecond	Milliseconds
Use case	Databases, boot volumes, applications	Backups, media, data lakes
Modification	Change individual blocks	Must re-upload entire object

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EBS Key Concepts

Volumes

An EBS volume is a virtual disk that you attach to an EC2 instance. Key characteristics:

• Persistent — data survives instance stop/start (unlike instance store).
• AZ-scoped — a volume exists in a single Availability Zone and can only be attached to instances in the same AZ.
• Attachable — most volume types support attachment to one instance at a time (io1/io2 support multi-attach).
• Resizable — you can increase volume size, change type, or adjust IOPS without downtime.

Snapshots

An EBS snapshot is a point-in-time backup of a volume, stored in S3 (managed by AWS). Snapshots are:

• Incremental — only changed blocks since the last snapshot are saved.
• Region-scoped — stored within the region but can be copied to other regions.
• Used to create new volumes — launch a volume from a snapshot in any AZ within the region.

# Create a snapshot
aws ec2 create-snapshot --volume-id vol-0123456789abcdef0 --description "Daily backup"

# Create a volume from a snapshot
aws ec2 create-volume --snapshot-id snap-0123456789abcdef0 --availability-zone eu-west-2a --volume-type gp3

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EBS Volume Types

EBS offers four main volume types, divided into two categories: SSD-backed (for transactional workloads) and HDD-backed (for throughput-intensive workloads).

SSD-Backed Volumes

Type	Name	Max IOPS	Max Throughput	Use Case
gp3	General Purpose SSD	16,000	1,000 MB/s	Boot volumes, dev/test, general workloads
gp2	General Purpose SSD	16,000	250 MB/s	Legacy general purpose (gp3 recommended)
io2 Block Express	Provisioned IOPS SSD	256,000	4,000 MB/s	Mission-critical databases (SAP HANA, Oracle)
io2	Provisioned IOPS SSD	64,000	1,000 MB/s	Databases needing sustained high IOPS
io1	Provisioned IOPS SSD	64,000	1,000 MB/s	Legacy provisioned IOPS (io2 recommended)

HDD-Backed Volumes

Type	Name	Max IOPS	Max Throughput	Use Case
st1	Throughput Optimised HDD	500	500 MB/s	Big data, log processing, data warehousing
sc1	Cold HDD	250	250 MB/s	Infrequent access, lowest cost