A method, apparatus, and article of manufacture containing instructions
for processing multiple point-in-time consistent data sets. The method
consists of creating multiple point-in-time data sets associated with a
backup appliance which is associated with backup storage. Upon the
transfer of a first update from a primary storage controller to the
backup appliance, a determination is made whether the update affects data
stored in the backup storage has been unchanged following the creation of
the respective data sets. If the update does affect data which is
unchanged following the creation of a data set, the current, non-updated
data is read from the backup storage. A copy of the current, non-updated
data thus read from the backup storage is stored in a storage location
which can be one of the data sets or an independent memory location. In
addition, pointers are associated with the remaining applicable data sets
and directed to the copy at its storage location. Subsequently, the
update is applied to the data on the backup storage device. In the event
an update is subsequently transferred from the primary storage controller
to the backup appliance which affects data stored in backup storage which
has already been changed since the creation of an applicable data set, no
further data is written to the applicable data set and the update is
applied to the backup storage.