Random r = getRandom();
        while ( p < length ) {
            randBytes(r, buffer);
            int w = Math.min(bufSize, (int) ( length - p ));
            os.write(buffer, 0, w);
            p += w;
        }
        log.debug("Write " + length + " took " + ( System.currentTimeMillis() - start ));
    }


    static final void randBytes ( Random r, byte[] buffer ) {

            int read = is.read(buffer, 0, rs);
            if ( read < 0 ) {
                fail("Unexpected EOF");
            }

            byte verify[] = new byte[read];
            ReadWriteTest.randBytes(r, verify);
            byte actual[] = Arrays.copyOfRange(buffer, 0, read);

            assertArrayEquals("Data matches at offset " + p, actual, verify);

            p += read;
        }