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Azure SQL servers never need to be backed up, as this is already done for you. You may wish, however to opt-in to geo-redundant storage to replicate a copy of the database(s) to another other Azure datacenter(s) in case of natural disaster or other catastrophe.
By default, the Azure SQL servers are replicated in real-time to 3 different failover nodes in different fault zones in the datacenter, and should one of those machines, or one of the components, fail - then the requests are automatically redirected to one of the failover machines and a new machine provisioned automatically to replace the failed machine. If you choose geo-redundant storage, then the same applies to the datacenters replicated to.
You may wish to extend the data retention period for the point-in-time backups beyond the standard 7 to 35 days. Up to 10 years of data retention of point-in-time restore is available.
You can also manually export the database to a storage blob or even local file system if desired.
MS Azure Calculator
If you haven’t already, you can use the Azure pricing calculator to see the pricing options - https://azure.microsoft.com/en-au/pricing/calculator
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