I was located in the Bay Area so my screening interview was also onsite. It was a one hour interview with the a senior executive at PernixData. The question first involved coding up a problem and then went on to more of a design problem. I think I did fairly well at this as I did receive an invite for onsite.
There were two sets of onsite interviews - 3 hours each.
Each interview focused on different aspects. Kernel space knowledge, synchronization, storage system design, complexity of algorithms, programming questions. Each involved writing code on the whiteboard.