What is FlashCache
FlashCache is a general purpose writeback block cache for Linux. That means you can use it with your Solid State Drive (SSD) or Flash Drive to speed up your hard disk access. Think of it as a software based Hybrid Drive. It was developed by Facebook to help run Facebook.
What is Dracut
Dracut is an initramfs infrastructure. It provides some important glue to help during the boot phase of Red Hat Linux (Fedora, RHEL and by extension, CentOS). It is interesting as it uses udev to coordinate its work of finding and mounting the root filesystem.
dracut-flashcache provides a ready to use way for using FlashCache on your root (/) filesystem or LVM Physical Volume which makes it suitable for general Linux desktops/workstations.
There are a number of steps required to get dracut-flashcache running. Basic instructions are shown here with links to more detailed instructions. At the moment, only EL6 is supported (RHEL6 & CentOS-6)
Although it is not a bug in dracut-flashcache (AFAIK), there is a bug somewhere in the interaction between flashcache and some media (tv) drivers. I can't explain why these drivers should cause problems but for me, they do. The FlashCache bug tracker has the details.