The idea to use SSD/Flash as a cache is not new, and there are
different solutions for this, both OpenSource like L2ARC for ZFS
and Flashcache from Facebook, and proprietary, like
directCache from Fusion-io.
They all however have some limitations, that’s why I am considering to have L2 cache on a database level, as an extension to InnoDB buffer pool.
Fortunately, there is a project in progress …