AWS TL;DR: EBS Volumes

AWS EBS Volumes

/tldr: Network-attached, persistent block storage for EC2 instances.

Block Storage High Performance Persistence

1. Core Concepts: Block Storage

EBS Volumes are essentially virtual hard drives attached to an EC2 instance over the network. Unlike S3 (Object Storage), EBS is **Block Storage**, meaning the operating system sees it as a raw, formatted disk.

Persistence and Lifecycle

**Persistent:** EBS data persists even after the EC2 instance is stopped or terminated (unless configured otherwise).
**Boot Volume:** The root volume (OS drive) is always an EBS volume. By default, it is deleted when the instance is terminated.
**One-to-One:** A volume can only be attached to a single EC2 instance at a time (unless using Multi-Attach on specific IOPS types).

AZ Dependency (Crucial)

EBS volumes are AZ-specific. They must reside in the same Availability Zone as the EC2 instance they are attached to.

**Durability:** EBS is replicated within its AZ (99.8% - 99.9% availability), but it does **not** span AZs automatically.
**Migration:** To move a volume across AZs, you must create a **Snapshot** first.

2. Volume Types: Performance Tiers

EBS offers different volume types optimized for transactional workloads (SSD) or sequential throughput (HDD).

SSD-Backed (Transactional)

Optimized for frequent read/write, high IOPS.

**General Purpose (GP3):** Default choice, cost-effective for most workloads. Baseline 3,000 IOPS and 125 MB/s throughput, burstable.
**Provisioned IOPS (IO2):** Highest performance, mission-critical applications (e.g., large databases). You explicitly define IOPS and throughput targets.

HDD-Backed (Throughput)

Optimized for large, sequential data access.

**Throughput Optimized (ST1):** Frequently accessed, large sequential workloads (e.g., ETL, logs, data warehousing).
**Cold HDD (SC1):** Least expensive, infrequent access, large sequential data (e.g., archival storage where data access is rare).

3. Snapshots: Backup & Recovery

An EBS **Snapshot** is the key to backing up and moving EBS data.

How They Work

**Incremental:** Only blocks that have changed since the last snapshot are stored. This saves storage space and reduces backup time.
**Storage Location:** All snapshots are transparently stored on **AWS S3**.
**First Snapshot:** The first snapshot is a full copy; subsequent snapshots only store the delta.

Use Cases

**Recovery:** Restore a volume from a snapshot if the primary volume fails.
**Cross-AZ Migration:** Copy a snapshot to a different AZ, then create a new volume from that copied snapshot.
**AMI Creation:** Snapshots are used in the process of creating custom Amazon Machine Images (AMIs).

# AWS CLI command to create a snapshot
aws ec2 create-snapshot --volume-id vol-0a1b2c3d4e5f6g7h8 --description "Daily backup of WebApp Volume"

EBS is the performance engine; Snapshots are the safety net.