Zend Cache documentation
To pass Zend Cache options to concrete5 we can define two settings in /config/site.php
Both of these settings take in a serialized array of Zend Cache options.
For example. Lets say we have a site that have 200,000 files or objects that could potentially be cached. Having all of these in one directory can make for a long night of deleting and also has an effect on performance. So let's divide these up in some handy sub directories with the Zend Cache backend option "hashed_directory_level" by adding this to our config/site.php file.
define('CACHE_BACKEND_OPTIONS', serialize(array('hashed_directory_level' => 2)));
That's all there is to it!
There are many other front and back end options available. Consult the Zend Cache documentation above for more information.