Prevent Redis Cache from clearing ALL keys
You can set your default Drupal key up (in settings.php) then have your custom keys set to not expire or last longer. 

$conf['cache_prefix'] = array('default' =&gt; 'your-redis-key');


See Redis config file for documentation on how to setup max memory and such: https://raw.githubusercontent.com/antirez/redis/2.8/redis.conf

By doing this you would be setting up the policies that Redis will use to clear the cache out and what to clear. It has to clear eventually or it will become unstable, it's just cache after all :) I wouldn't be depending on it to stay that's for sure.