As I mentioned in my talk An Overview of Flash Storage for Databases I see in the near and middle term future a lot of interest for using Flash storage in Level 2 caching level. The price-capacity trade-off makes Flash as the very good fit for a cache layer.
Actually it is not the new idea, and it was implemented in L2ARC ZFS for two years already.
It is also described in ACM article “Flash storage memory” by Adam Leventhal.
So I am exciting to see it is available for Linux now. Paul Saab and Mohan Srinivasan from Facebook released Flashcache, which allows to use Flash as cache in front of regular hard drives.
The implementation is based on dm-cache and introduces a new block level device to the system, which you use instead of a regular partition.
I congrats Facebook with implementation of great idea and I am happy to see Facebook releases it under GPL license. I am working on builds to see if we can provide binaries for different platforms.
And, I also see another idea implemented by David Jiang
http://code.google.com/p/david-mysql-tools/wiki/innodb_secondary_buffer_pool, it allows to use a file on Flash partitions as L2 cache for InnoDB buffer pool. I see a lot of potential here, and I am going to evaluate it for including into XtraDB.