And with SSD's and HDD memory plus OS disk caching, HDD storage can be very fast. It works great as a simple key/value storage. Duplication (read slaves) and sh

And with SSD's and HDD memory plus OS disk caching, HDD storage can be very fast. It works great as a simple key/value storage. Duplication (read slaves) and sharding also works great. Modern file systems such as ZFS also helps speed things up and provides nice features like "snapshots" that isn't even possible in modern databases.