Physical isolation – When possible, Azure prefers at least 300 miles of separation between datacenters in a regional pair, although this is not practical or possible in all geographies. Physical datacenter separation reduces the likelihood of natural disasters, civil unrest, power outages, or physical network outages affecting both regions at once. Isolation is subject to the constraints within the geography (geography size, power/network infrastructure availability, regulations, etc.).
Platform-provided replication - Some services such as Geo-Redundant Storage provide automatic replication to the paired region.
Region recovery order – In the event of a broad outage, recovery of one region is prioritized out of every pair. Applications that are deployed across paired regions are guaranteed to have one of the regions recovered with priority. If an application is deployed across regions that are not paired, recovery may be delayed – in the worst case the chosen regions may be the last two to be recovered.
Sequential updates – Planned Azure system updates are rolled out to paired regions sequentially (not at the same time) to minimize downtime, the effect of bugs, and logical failures in the rare event of a bad update.
Data residency – A region resides within the same geography as its pair (with the exception of Brazil South) in order to meet data residency requirements for tax and law enforcement jurisdiction purposes.
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