Amazon S3 is the central object store of the AWS platform, advertising eleven nines of durability (99.999999999%) by automatically spreading data across multiple devices and facilities within a region. A bucket is globally named, but the data it holds is regional, and by default an account can create up to 100 buckets (1,000 after a quota increase). Individual objects can grow to 5 TB, and multipart upload is recommended above 100 MB and required above 5 GB. S3 now offers strong read-after-write, list, and overwrite/delete consistency, which simplifies application design compared to the older eventual-consistency model.
S3 provides a family of storage classes that trade cost against retrieval latency. Standard is for hot data, and S3 Intelligent-Tiering automatically moves objects between tiers when access patterns change with no retrieval charges, making it the right pick for unknown or shifting workloads. For colder data, S3 Glacier Flexible Retrieval (minutes to hours), S3 Glacier Instant Retrieval (milliseconds, very low cost), and S3 Glacier Deep Archive (12-hour retrieval, cheapest of all) cover the long tail. Lifecycle rules transition objects between classes over time so cost follows usage.
Protecting objects in S3 involves a small toolkit. Versioning plus MFA Delete guards against accidental deletion, and S3 Object Lock in Governance or Compliance mode enforces immutability for regulatory retention. Pre-signed URLs give third parties time-limited access to specific objects without making them public. Cross-Region Replication (CRR) and Same-Region Replication (SRR) both require versioning on the source and target buckets. When serving a private static site through CloudFront, an Origin Access Control (OAC) plus a tight bucket policy keeps the bucket non-public while still allowing the distribution to read it. For server-side encryption, you can choose SSE-S3 (S3-managed keys), SSE-KMS (KMS-managed with audit trails), or SSE-C (keys you supply).
Beyond S3, AWS offers shared file and block storage. Amazon EFS provides a shared POSIX file system that many EC2 instances can mount concurrently, ideal for lift-and-shift Linux workloads. FSx for Lustre delivers a high-performance parallel file system tuned for HPC. AWS Storage Gateway bridges on-premises environments with cloud storage through cached or stored volumes and file gateways, while Application Migration Service (MGN) handles block-level VM migration into EC2.