RegionSizeStore getRegionSizeStore() {
    return rs.getRegionServerSpaceQuotaManager().getRegionSizeStore();
  }
Computes total FileSystem size for the given {@link Region}.
@param r The region
@return The size, in bytes, of the Region.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/FileSystemUtilizationChore.java