Storage is ending in tiers
One basic rule of storage is don't keep items you need to access quickly in hard-to-get-at places: that's like keeping instant coffee in a safe. You suit the storage type to the type of item you want to store. One size does not fit all, and valuable data should not be stored on slow-speed disk drives along with ordinary data. The "hot" data - information that is needed often and fast - should be stored on fast disk drives, not slow ones. But these drives should not be cluttered with old data that no one will access in a blue moon. Disk drive array suppliers and storage administrators have understood this for years, but they still have to resolve the following: how is hot data to be identified, then moved from fast to slow storage, and how often should this be done?