What is Geo Redundant Storage (GRS)?
Geo-redundant storage (GRS) is designed to provide at least 99.99999999999999% (16 9's) durability of objects over a given year by replicating your data to a secondary region that is hundreds of miles away from the primary region. If your storage account has GRS enabled, then your data is durable even in the case of a complete regional outage or a disaster in which the primary region is not recoverable.
With GRS, the replica is not available unless Microsoft initiates failover to the secondary region. If Microsoft does initiate a failover to the secondary region, you will have read and write access to that data after the failover has completed.