Object Storage and Amazon S3
How S3 stores files as objects under keys, what its durability and consistency promises really mean, and how to control its costs.
What object storage is
Object storage stores whole blobs of data (images, videos, backups, logs) and finds each one by a name, not by a folder path on a disk. Amazon S3 (Simple Storage Service) is the best-known service; Google Cloud Storage, Azure Blob Storage, Cloudflare R2 and the open-source MinIO work the same way.
Three words to know:
- Bucket. A named container, globally unique across all AWS accounts, created in one region.
- Object. The data (up to 5 TB) plus metadata (content type, custom tags, size).
- Key. The object's full name, such as
photos/2026/10/cat.jpg. The namespace is flat. The/characters are just part of the string; the console draws "folders" by grouping keys with a common prefix.
You talk to it over HTTP: PUT to store, GET to read, DELETE to remove, LIST to enumerate keys.
| Object storage (S3) | Block storage (EBS) | File storage (EFS, NFS) | |
|---|---|---|---|
| Unit | Whole object | Fixed-size blocks | Files and directories |
| Access | HTTP API | Attached to one server like a disk | Mounted by many servers |
| Edit part of a file | No, rewrite all | Yes | Yes |
| Scale and cost per GB | Huge, cheapest | Limited, pricier | Medium |
| Good for | Media, backups, data lakes | Databases, boot disks | Shared home dirs, legacy apps |
1 of 9