An error in default configuration set autoclean to a value too large and the cache expiration time too low. Change the values: set the timeout for page to 1440 and autoclean to 60.
This configuration keeps the cache storage space much lower. To estimate if the number of cache files is too much, I need to know how many posts your blog has. Remember that every tag (if you use tags) is at least a page.
Traffic is another parameter to evaluate: users and bots trigger page caching on each request they do. High traffic on a bug blog leads to ahve many page cached.
Have you Global Translator active? If so, look at Hyper Cache configuration: there are some tips on the advanced options.
Have you changed the permalink structure recently? If so you are issuing a lot of redirects... disable the redirect caching.