you don't want things like ACL hitting disk if you can avoid it, however if you're already on rails i don't even know :) Although the opposite response may be

you don't want things like ACL hitting disk if you can avoid it, however if you're already on rails i don't even know :) Although the opposite response may be that you definitely want things like ACL to be transactional / persistent which may be a strong reason to specifically not use something like redis and use SQL, to each their own however