📝Durability is at odds with High Availability

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DeCandia…₂₀₀₇

Durability is often thought as a requirement for high availability—a write operation completes only when enough replicas persistently store the data, so it’s guaranteed to not get lost.

However, requiring more replicates to durably store data before completing operation increases response times and increases the risk of timing out, thus decreasing availability. In practice, it’s enough that data is disseminated between the replicas that will eventually store it durably, without blocking operation on persistent storage.