Flashcache is a module originally written and released by Facebook(Mohan Srinivasan, Paul Saab and Vadim Tkachenko) in April of 2010. It is a kernel module that allows Writethrough caching of a drive on another drive. This is most often used for caching a rotational drive on a smaller solid-state drive for performance reasons. This gives you the speed of an SSD and the size of a standard rotational drive for recently cached files. Facebook originally wrote the module to speed up database I/O, but it is easily extended to any I/O.
To install on CL6 server:
$ yum install flashcache --enaberepo=cloudlinux-updates-testing
To install on hybrid server:
$ yum install flashcache - --enablerepo=cloudlinux-hybrid-testing
More info on flashcache:
ArchLinux has a good page explaining how to use flashcache: