Durability

The guarantee that confirmed data is not lost. It comes from writing to disk, replicating across machines and zones, and keeping backups; eleven nines of durability means losing one object in a hundred billion per year.

Where it shows up in real systems

  • Object storage

    Practically unlimited capacity and eleven nines of durability, but each request takes tens of milliseconds and throughput is limited per key prefix. Put a CDN in front for public files; infrequent-access classes are cheaper to store but charge per retrieval.

    In production: Amazon S3, Azure Blob Storage, Google Cloud Storage, Cloudflare R2, MinIO

See it break, then fix it

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