As Brian said, you're asking a rather broad question. What exactly are you asking with regards to performance issues?
Did you have an application or actual proposed use in mind in sufficient detail to make this a question we can helpfully answer, or at least try to?
Have you talked to any of the relevant vendors in this space-- newcomers like Tegile, Nimble, Tintri, Nutanix, etc.? Or established ones, such as Equallogic, EMC, Netapp, Fusion-io,
Is commentary such as this sufficient...?
The harddisks and the SSD's are usually organized separately when it comes to the actual hardware disk sets, it's not a straight RAID10, if that's what you're asking. Now how the firmware manages the various controllers involved with the harddisk arrays and the SSD arrays is the tricky part...