Level 1 cache → RAM and then hdd. The cache levels will be dynamic but not initially (unless we can get it squeezed in). The idea is most recent cache is in RAM and then we have opportunities for very fast data access t recent data and in some cases I believe faster than local hdd (mg drive where transfer rates are 30-40 Mb/s). In code right now that cache I believe is on disk, but likely to be mmap file (issues with 32 bit though, of course).