Data Hazards in DiskRAM

R = Read A = After W = Write

RAR = no hazard
WAW = writes always complete in order with respect to other writes
RAW = hazard, but since I'm buffering writes, reads to the same location should be caught at the highest level.
- I need to take some care here to make sure that evictions from the buffer don't pass a later read.
WAR = hazard, since I buffer writes, writes don't get propagated, so as long as the write waits until the read checks the buffer, it should be OK.
- Again, if there is an eviction from the write buffer, that could cause problems with an earlier read.

Let each level handle coherency (pass ordering information or order bus)
Have a master which doesn't allow units to see transactions out of order if they are RAW or WAR