Understanding Cosmos DB availability

Azure Cosmos DB is built with availability in mind. The underlying database of a Cosmos DB account is written to four replicas with any given region – this is the default and minimal configuration in regard to availability.

You can optionally create one or more replicas of your databases in any Azure region that supports Cosmos DB. Replicas in other regions are also replicated within that region to four other replicas. For example, suppose you set up your Cosmos DB account to be multi-region across two regions. In that case, you will have eight replicas of your data – four in the primary and four in the secondary regions.

Although data within a region is replicated four times, it is not stored across Availability Zones by default. This is an optional configuration applied to a Cosmos DB account in regions that support high-Availability Zones.

Another factor to consider when using Cosmos DB with global replication is whether to...