Ordering data writes include a host computer providing a plurality of data
writes to a primary storage device, the primary storage device assigning a first
sequence number to data writes begun after a first time and before a second time,
the primary storage device assigning a second sequence number, different from the
first sequence number, to data writes begun after the second time, in response
to completion of all writes assigned the first sequence number, the primary storage
device transferring writes assigned the first sequence number to a secondary storage
device, and, in response to the primary storage device transferring all writes
assigned the first sequence number to the secondary storage device, the primary
storage device sending a commit message to the secondary storage device. Ordering
data writes may also include, in response to receiving a commit message from the
primary storage device, the secondary storage device storing the data writes having
the first sequence number.
