code: static Storage initializeGroup(Collection<Storage> group) {
          List<Storage> sorted = Ordering.natural().immutableSortedCopy(group);
          Storage primary = sorted.get(0);  // After sorting, the first storage in each group is the primary.
          if (!primary.isConsistent()) {
              // Dropping the primary drops the entire group (primary+mirrors), so 'primary' must be a mirror that
              // should have been dropped but was missed due to error conditions related to eventual consistency.
              return null;
          }
          for (Storage storage : sorted) {
              storage._group = sorted;
          }
          return primary;
      }
docs: Post-construction initialization links all non-dropped members of group together.  Returns the primary member
  of the group, other members are mirrors.