Hi Hiro! I attached a version of the current system layout, things will change a the lowest level for 0.20 but the other things should stay the same.
At the very bottom we are going to have something called a Hfile which is basically a list of something called KeyValues. The KeyValues are a byte [] including the key, row/family/column/timetsamp/type, and the value. What makes it column oriented at this level is that families are physically stored together. Depending on how big a row is you can different number of rows covered in a storefile. Hope this helps. Regards Erik
