public static HRegionFileSystem createRegionDir(Configuration configuration, RegionInfo ri,
    Path rootDir) throws IOException {
    FileSystem fs = rootDir.getFileSystem(configuration);
    Path tableDir = CommonFSUtils.getTableDir(rootDir, ri.getTable());
    // If directory already exists, will log warning and keep going. Will try to create
    // .regioninfo. If one exists, will overwrite.
    return HRegionFileSystem.createRegionOnFileSystem(configuration, fs, tableDir, ri);
  }
Create the region directory in the filesystem.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java