int maxValueSize(final int keySize) {
        final int pageSize = _volume.getPageSize();
        final int reserveForKeys = (KEYBLOCK_LENGTH + TAILBLOCK_HDR_SIZE_INDEX) * 3 + maxStorableKeySize(pageSize) * 2
                + keySize;
        return (pageSize - HEADER_SIZE - reserveForKeys) / 2;
    }