Methods and apparatus for obtaining consistency of redundant data after a
failover event. In one aspect, a redundant data storage system has a
first data storage facility that initially acts as a primary facility for
storage requests and a second data storage facility that initially acts
as a secondary facility for the storage requests. The second data storage
facility is conditioned to assume the role of the primary facility in
response to a failover event. The first data storage facility is
conditioned to assume the role of the secondary facility, which includes
sending a copy of data committed at the second data storage facility to
the first data storage facility. The copy of data includes a version of
data committed at the second storage facility.