A technique is described to enable exclusive control on a file basis in a storage
system while remote double recording is performed between storage controllers.
A first shared-file controller has a table that stores control information used
for excluding read and write to that file on a file basis. When the shared-file
controller receives a data write request, it sets access to the file as exclusive,
and then issues a command to a second shared file controller to set control information
for that file. After data is written into a storage medium and mirrored to a second
storage medium, a copy of the file management information is stored in memories
of the shared-file controllers. The consistency of the file management information
is maintained between the two file controllers by copying the file management information
over the network.
