You can open any output file descriptor passing the flag O_APPEND (see the open(1) reference page). Asynchronous write requests to a file opened with O_APPEND are executed in the sequence of the calls to aio_write() or the sequence they are listed for lio_listio(). You can use this feature to ensure that a sequence of records is appended to a file in sequence.
For files that support lseek(), you can specify any order of operations by specifying the file offset in the aiocb. The asynchronous process executes an absolute seek to that offset as part of the operation. Even if the operations are not performed in the sequence they were requested, the data is transferred in sequence. You can use this feature to ensure that multiple requests for sequential disk input are stored in sequential locations.
For non-disk input operations, the only way you can be certain that operations are done in sequence is to schedule them one at a time, waiting for each one to complete.