AWS S3 (Simple Storage Service) is a cornerstone of cloud storage, offering a vast, scalable, and highly durable object storage service. This deep dive will explore the system design considerations, key components, and trade-offs involved in building a system like S3.

Object Store

High-Level Design (HLD)

• Stores data as **objects (key-value pairs)** where the key is the object's unique identifier (e.g., "image.jpg") and the value is the actual data.
• Provides a **flat namespace** within a bucket.
• Supports **metadata** associated with each object.
• Highly scalable and designed for **large datasets**.

Low-Level Design (LLD)

• **Metadata Storage:**
  • **Consistent Hashing** (e.g., Consistent Hashing) to distribute metadata across multiple servers for high availability and scalability.
  • **Replicate metadata** across multiple availability zones for fault tolerance.
  • Use a distributed database (like **Cassandra** or **DynamoDB**) for efficient metadata storage and retrieval.
• **Object Storage:**
  • Store object data in **chunks** across multiple servers within an availability zone.
  • Utilize **erasure coding techniques** (like Reed-Solomon) to provide data redundancy and fault tolerance.
  • Implement efficient **data placement algorithms** to optimize read/write performance and minimize data transfer.

File Store

High-Level Design (HLD)

• Stores data in a **hierarchical structure** (directories and files) similar to a traditional file system.
• Supports operations like create, read, write, delete, and move files and directories.
• Provides a more familiar interface for users accustomed to file systems.

Low-Level Design (LLD)

• **Metadata Storage:**
  • Utilize a distributed file system (like **HDFS**) to store metadata (file names, directories, permissions).
  • Implement a **metadata server** to handle metadata operations and maintain data consistency.
• **Data Storage:**
  • Store data in chunks across multiple servers.
  • Implement **data replication** and **fault tolerance mechanisms**.

Block Store

High-Level Design (HLD)

• Stores data as a collection of **blocks** (fixed-size units of data).
• Provides low-level storage abstraction for building higher-level storage services (e.g., file systems, databases).
• Offers high performance for random read/write operations.

Low-Level Design (LLD)

• **Data Storage:**
  • Divide the storage into logical units (e.g., 4KB blocks).
  • Assign each block to a specific storage device (e.g., **SSD**, **HDD**) based on performance and cost requirements.
  • Implement **data striping** and **replication** across multiple devices for fault tolerance and performance.

AWS S3: A Deeper Dive

• **Bucket:** A fundamental unit of storage in S3. Each bucket has a globally unique name.
• **Object:** A data unit within a bucket. Objects can be any type of data (images, videos, documents, etc.).
• **URI:** A unique identifier for an object within S3 (e.g., `s3://bucket-name/object-key`).
• **Durability:** S3 offers industry-leading durability (99.999999999%) with data replicated across multiple availability zones.
• **Availability:** S3 provides high availability with multiple availability zones and redundant infrastructure.

AWS Ecosystem

S3 seamlessly integrates with other AWS services, such as:

• **EC2:** For running applications that interact with S3.
• **Lambda:** For serverless functions that process data stored in S3.
• **Glacier:** For archiving infrequently accessed data.
• **EBS:** For persistent storage for EC2 instances.