1. That seems well in line given the vagaries of HDD capacities. 2. If you have 3 drive failures, yes, data is destroyed. In that case, you would contact Isilon and they might be able to help you recover it. Note that it wouldn't be all data destroyed, just data that was striped (at least partially) onto those 3 drives. It's important to replace drives quickly at +2d:1n. 3. If SSD fails, the system should be just fine, particularly if you're using L3. If you're using metadata on SSD schemes, the data is either protected on HDD (metadata read) or on other SSDs. I don't recall exactly, but I suspect it's probably at 4x mirroring for metadata at +2d:1n.
Hi all!  I have some question for Isilon, please help me answer, thanks! - I have 3 node, in one node have 35 drive (2TB), but when I show in system, I onnly see total 181TB, why? - I check protect level +2d:1n => 2 drives or 1 node failure. In case, system have 3  drives failure, data destroyed? and how to recover? - SSD failed, how is system? 
Question for Isilon data protect level