The RedisCache uses Redis::SERIALIZER_IGBINARY. See https://github.com/doctrine/common/blob/master/lib/Doctrine/Common/Cache/RedisCache.php line 47.
The problem is that the php Redis extension can be compiled without IGBINARY support. In that case, this code causes a fatal error because the constant does not exist.
The DotDeb package of php5-redis (often used on Debian systems) for example comes compiled without IGBINARY support.
The code should probably check if the constant exists. If not, the default to Redis::SERIALIZER_PHP