Squid external overview

aufs
What is it?
Based on pthreads
Has a set of 'worker threads' which complete IO requests

Pros
Very fast on platforms which support kernel pthreads
Has the potential to be even faster

Cons
Too many memory-memory copies due to its original design (it was designed to not integrate into squid at all)
Most threads spend their time waiting for the kernel to finish disk IO, since IO on a single disk will only finish one at a time!
Very basic write and read clustering
There are no per-storedir threads, only a global 'pool'