A network storage filer implements a four-phase commit protocol to
coordinate consistency points among a group of volumes (a "group
consistency point") such that, upon recovery, all volumes of the group
reflect consistency points taken at the same time. The filer records
progress at each phase while creating the consistency points of the
volumes. Upon recovery, the same or a different filer uses the last
recorded progress indicator to ascertain whether the consistency points
were completed on all of the volumes in the group. If all the volume
consistency points of the group consistency point were completed, the
filer users the volume consistency points to mount the volumes.
Otherwise, the filer uses an earlier group consistency point to mount the
volumes. In either ease, the volumes are consistent with each other.