@CanIgnoreReturnValue
  public long write(long pos, Iterable<ByteBuffer> bufs) throws IOException {
    long start = pos;
    for (ByteBuffer buf : bufs) {
      pos += write(pos, buf);
    }
    return pos - start;
  }
Writes all available bytes from each buffer in {@code bufs}, in order, to this file starting at
position {@code pos}. {@code pos} may be greater than the current size of this file, in which
case this file is resized and all bytes between the current size and {@code pos} are set to 0.
Returns the number of bytes written.

@throws IOException if the file needs more blocks but the disk is full
jimfs/src/main/java/com/google/common/jimfs/RegularFile.java