In the conventional storage system, consistency is ensured only for
writing from a single storage. Asynchronous remote copying and local
replication are also alternately suspended in the conventional system, so
that the suspension time increases and the volume in which consistency is
obtained becomes old. Two local replicas are prepared, for a volume
containing stored data that is transferred from the main site by
asynchronous remote copying, in the storage at the sub-site. Each pair of
local replicas is alternately suspended by a time-specific suspension
command according to the time of the timestamp attached to the write
data, and replica data in which the time sequence is secured is
continually prepared. When a failure occurs at the main site, the data is
recovered using the replica data.