ZFS handles the three-tiered model well (with the L2ARC implementation). Also, the authors of this paper didn't consider the "write-limited" implementation that the ZFS authors use: they write at a fixed rate to SSD (e.g., 8MB/sec) and pull entries near the end of the RAM-based cache (i.e. the ones that are about to expire). Still, quite a great paper.<p><a href="http://www.sun.com/emrkt/openstorage/0309engineers.html?cid=e8017" rel="nofollow">http://www.sun.com/emrkt/openstorage/0309engineers.html?cid=...</a>