flash pci express versus ssd hard disks

http://www.dcig.com/2012/05/fusion-ios-take-on-emcs-vfcache.html


 You cannot put the flash on a PCI-Express card and call it 'good.' All they have done is taken the metal coverings off of flash drives and stuck them on a RAID controller. To be like Fusion-io, you also have to eliminate the large storage protocols and have the CPU interact with flash natively over the PCI-Express bus. 

Flash drives have been speaking to the CPU through PCI-Express since they have first launched. They are only two ways to talk to the CPU - system bus (PCI-Express) or memory bus. That's it. There is no other way. Everything, host bus adaptor, RAID controller, graphics card, all communicate with the CPU through PCI-Express. 

So just because you put the flash drives on a RAID controller and put them in the PCI-Express slot, it is no different than a RAID controller with eight (8) drives hanging off of it.  You are still going to have a ton of context switching, which can cause dramatic and unpredictable swings in latency.