code: Delta newMoveStart(Storage src, String destUuid, String destPlacement, int destShardsLog2) {
          return Deltas.mapBuilder()
                  .update(STORAGE.key(), Deltas.mapBuilder()
                          .update(src.getUuidString(), Deltas.mapBuilder()
                                  .put(Storage.MOVE_TO.key(), destUuid)
                                  .build())
                          .put(destUuid, storageAttributesBuilder(destPlacement, destShardsLog2, src.isFacade())
                                  .put(StorageState.MIRROR_CREATED.getMarkerAttribute().key(), now())
                                  .put(Storage.GROUP_ID.key(), src.getGroupId())
                                  .build())
                          .build())
                  .build();
      }
docs: First step in a move, creates the destination storage and sets up mirroring.