Recently, Dell announced the newest members of its EqualLogic PeerStorage line of virtualized iSCSI arrays: the PS6000XVS and PS6010XVS. Unlike the other PeerStorage arrays (which are either entirely SATA, SAS, or SSD), the XVS models mix eight SSDs and eight 15,000-RPM SAS disks in the same enclosure, giving you tiered storage in a single box.
Mixing two vastly different types of storage media in the same shelf isn't that unusual. Here's what's out of the ordinary: The XVS arrays automatically load-balance heavily used data blocks onto SSD while leaving less-used blocks on the SAS disk. In theory, this is an excellent idea. It should allow the array to adapt very quickly to changing I/O patterns and provide the best performance possible from its mix of very fast, but small SSDs and comparatively slow, but much larger SAS disks.
[ Looking to reduce your storage requirements? See InfoWorld's comparative review of four storage appliances that use data deduplication technology. | Also check out Matt Prigge's High-Availability Virtualization Deep Dive. ]
Take, for instance, the task of providing storage to a heavily used Microsoft SQL database. In most cases, you'd combine high-speed disk for the data volumes and, if needed, SSD space for transaction logs and tempdb. The XVS arrays attempt to make these sorts of architectural decisions unnecessary: The array knows best and can put your data on the storage media it deserves to be on.
Or does it?
I don't know about you, but having unseen software make decisions for me about what data deserves to be where gives me the willies. Sure, I'm all for anything that can make my job easier and yield better overall performance. But giving up control to a load-balancing algorithm or automation engine requires a level of trust I and many others like myself struggle with. And I don't think such discomfort is limited to storage admins, server admins, or even technologists in general.
As both an aviation and technology enthusiast, I get a certain amount of glee from reading stories about airline pilots who make the transition from largely mechanical aircraft such as the Boeing 737 to the heavily automated Airbus A319/A320. Veteran Airbus captains often sit quietly in the left seat and wait for the newly minted First Officer to ask, "What's it doing now?"