Task Statement 2.2: Design highly available and/or fault-tolerant architectures.

📘AWS Certified Solutions Architect – (SAA-C03)

1. What Are Storage Options in AWS?

Storage options are the different services AWS provides to store data. Each service is designed for specific use cases and has different:

Performance
Availability
Durability
Replication behavior
Cost

2. Key Storage Services You Must Know for the Exam

2.1 Amazon S3 (Simple Storage Service)

What it is:

Object storage for files, backups, logs, media, etc.

Key Characteristics:

Durability

11 9’s durability (99.999999999%)
Data is automatically stored across multiple devices and facilities

Availability

Typically 99.99% availability

Replication

Automatically replicates data across multiple Availability Zones (AZs) in a region
Optional replication:
- Same-Region Replication (SRR)
- Cross-Region Replication (CRR)

Storage Classes

Standard (frequent access)
Intelligent-Tiering
Standard-IA (Infrequent Access)
One Zone-IA (single AZ)
Glacier (archival)

2.2 Amazon EBS (Elastic Block Store)

What it is:

Block storage used with EC2 instances (like a virtual hard disk)

Key Characteristics:

Durability

Data is replicated within a single Availability Zone
Durable but not as resilient as S3 across AZs

Availability

Depends on the AZ
If AZ fails → volume becomes unavailable

Replication

Automatic replication inside the AZ
Manual replication:
- Snapshots to S3
- Copy snapshots across regions

Performance

High-performance (SSD, HDD options)

2.3 Amazon EFS (Elastic File System)

What it is:

Shared file storage for multiple EC2 instances

Key Characteristics:

Durability

Stored across multiple AZs automatically

Availability

Highly available (regional service)

Replication

Built-in multi-AZ replication
Optional cross-region replication

Use Case

Multiple servers accessing the same files

2.4 Amazon FSx

What it is:

Managed file systems (Windows, Lustre, NetApp ONTAP, OpenZFS)

Key Characteristics:

Depends on the file system type
Can support multi-AZ deployment
High performance for specialized workloads

2.5 Instance Store

What it is:

Temporary storage attached to EC2

Key Characteristics:

Durability

Not durable
Data lost when instance stops or fails

Availability

Only available while instance is running

Replication

No replication

2.6 Amazon S3 Glacier

What it is:

Low-cost archival storage

Key Characteristics:

Durability

Same as S3 (11 9’s)

Availability

Lower availability than standard S3

Retrieval

Slower access (minutes to hours)

3. Core Concepts You MUST Understand

3.1 Durability vs Availability

Durability

Measures how safe your data is from being lost
Example: If hardware fails, is your data still safe?

Availability

Measures how often your data can be accessed

Exam Tip:

S3 → Very high durability
EBS → High durability but limited to one AZ
Instance Store → No durability

3.2 Replication

Replication means making copies of data to improve fault tolerance.

Types of Replication in AWS

1. Within Availability Zone

Example: EBS replicates data inside the same AZ
Protects against disk failure

2. Multi-AZ Replication

Example:
- S3
- EFS
Protects against AZ failure

3. Cross-Region Replication

Example:
- S3 CRR
- EFS replication

Used for:

Disaster recovery
Global applications

3.3 Storage Types Comparison

Feature	S3	EBS	EFS	Instance Store
Type	Object	Block	File	Block
Durability	Very High	High	Very High	Low
Multi-AZ	Yes	No	Yes	No
Replication	Auto (multi-AZ)	AZ only	Multi-AZ	None
Persistence	Yes	Yes	Yes	No

4. High Availability and Fault Tolerance Design

To design fault-tolerant systems, you must:

Use Multi-AZ Storage

S3 and EFS automatically handle AZ failures
EBS requires backup strategy

Add Backup and Replication

EBS → Use snapshots
S3 → Enable CRR for disaster recovery
Databases → Enable Multi-AZ

Avoid Single Points of Failure

Do NOT rely on:
- Single EBS volume
- Instance Store

Combine Storage with Compute

Example architecture:

EC2 + EBS → Use snapshots
Shared workloads → Use EFS
Static data → Use S3

5. Important Exam Scenarios

Scenario 1:

Need highest durability and multi-AZ storage

✅ Answer: S3

Scenario 2:

Need low-latency storage attached to EC2

✅ Answer: EBS

Scenario 3:

Need shared file system across multiple EC2 instances

✅ Answer: EFS

Scenario 4:

Need temporary high-speed storage

✅ Answer: Instance Store

Scenario 5:

Need disaster recovery across regions

✅ Answer:

S3 CRR
EBS snapshot copy
EFS replication

6. Key Exam Tips (VERY IMPORTANT)

S3 = Most durable storage
EBS = Single AZ only
EFS = Multi-AZ shared storage
Instance Store = Temporary
Replication improves fault tolerance
Snapshots = backup mechanism for EBS

7. Quick Memory Summary

Durability = Data safety
Availability = Data access
Replication = Copying data for protection