Our latest MySQL white paper is Improving Percona Server performance with Flashcache on the Virident tachIOn Drive. (Virident funded the research, but as always, we wrote the report ourselves.)
The conclusion is that Flashcache can be good for read-heavy workloads, but more research is needed to understand its performance characteristics on write-heavy workloads. We explain the details of exactly how good and under what circumstances. We also developed some guidelines for sizing and pricing, to serve as advice for those interested in deploying Flashcache as a way of getting some of the benefit of flash without all of the cost, or the size limitations.
Baron,
“When we chose the results with the best improvement over RAID storage alone, where the working set is at least
50% larger than the buffer pool, we found that the improvement over RAID is not as dramatic as the read-only improvement.”
Can some one explain why the above observation is?
For example. Given 200GB working data set, 100GB RAM, 400GB Flashcache
If the 200GB working data set is on 400GB Flashcache, the performace should still be much higher than using RAID alone.
We need more research to understand this. It may have to do with the way dm is implemented in the Linux kernel.