Erasure coding not replication

10 data shards + 4 parity shards. Can lose any 4 shards, recover. More storage-efficient than 3x replication (1.4x vs 3x overhead).

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Erasure coding not replication

10 data shards + 4 parity shards. Can lose any 4 shards, recover. More storage-efficient than 3x replication (1.4x vs 3x overhead).

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Multi-AZ placement

Shards distributed across 3+ AZs. Whole AZ can fail — object still retrievable.