Has anyone tried a dual ssd fusion drive? I have two 128 gb crucial drives, a M4 and V4. I'd like to create a fusion drive in Mavericks with the M4 as the "lead"(?) drive. Any advice ? Is it worth it?
I have a V4 SSD I use as a portable drive so I can understand the dilemma; it's random access performance (especially read + write together) is horrible, still much better than a USB thumb stick, but nothing like better SSDs. But is there no way you could just get a cheap(-ish) HDD to use instead?
As for whether it works; I'm not sure Fusion Drive does any kind of profiling of drives, I think it's currently a bit more primitive than that. i.e - if you create a core storage volume and the first drive added is an SSD, then you get a Fusion Drive, otherwise you don't.
So it should work as long as you add the M4 first, and in the particular case of an M4 feeding into a V4, it could work pretty well actually. I'm not sure you're likely to find many people who've tried it though, so it's probably a case of just trying it yourself and seeing how it turns out; make sure you put enough data on the volume to exceed the M4's capacity, and see how the performance measures up and go from there.
I wouldn't recommend an SSD RAID at all for an M4 + V4; while you will nearly double the speed for stuff the V4 is fine at (continuous single read/write), anything that the V4 struggles with will cripple the M4's performance. The only RAID option really would be concatenating the drives, but while you might lessen the V4's performance issues by spreading your data out, you can't guarantee where your data will end up; applying a system update could end up putting system files on the V4 for example. If you absolutely need to combine these drives into one volume then your Fusion Drive idea is definitely the best one to try.