Caching in Prestashop 1.6 (idk about 1.7) is fucking bullshit. I don't know who made it but he surely must be an idiot. There is no way that the cache is going to speed up your website after a few days of using it.
Memcache/d - For some strange reason, it gets slower and slower after just a few hours. There is literally almost no entries in memcache, but it becomes slower than without cache? WTF
APC - Do you have multiple websites running? You are out of luck. Do you make a change to your website? Restart PHP to see changes. WTF
Redis - Same as APC, but you have to run flushall manually. WTF
CacheFS - God, this is a fucking monstrosity. It rapes the storage drives so hard, it is like running a fucking benchmark nonstop. 400-600MB writes are completely "normal". I have no idea, what is it doing tho. I would expect that writing ~3MB file to disk doesn't require over 100MB/s disk write for 2(!) or more seconds. Also, it doesn't clean up after itself, so after a few days you are out of disk inodes and you have to setup CRON to clean this shit up regularly. In the end, it makes your website fast, but only as long as you have <={number of CPU cores} customers shopping. Then, it becomes a complete disaster and requests are taking 5+ seconds to finish.