Well, I just learned from Github, that maybe you will implement Redis in the future release but you don’t have any other mean to cache the database.
I’m new to the redis stuff, I just installed it on my server and the WP plugin too. BUT, so you know, W3TC needs to be updated soon as it gives error to Redis and memcache and HHVM. Example bellow for redis:
[Fri Nov 14 17:43:43 2014] [hphp] [1734:7f221cbff700:1:000001]  \nWarning: Parameter 1 to W3_Plugin_TotalCache::ob_callback() expected to be a reference, value given in /var/www/devly.co/htdocs/index-wp-redis.php on line 128 root@devly:~#
Also, if I installed redis, do I still need to keep memcached? If I want to setup pagespeed to go with redis, how do I do that? database cache I still use it with memcached in W3TC.