Anyway, I was reading about the product on The Register, and I was particularly struck by this:
The EasyTier feature watches the data I/O pattern and moves the most active sub-LUN-sized pieces of data, called extents, up to the SSD tier for the fastest response.
"Having 6 per cent of the capacity being solid state can deliver around 200 per cent performance improvement," said Doug Balog, an IBM VP and the disk storage business line executive. "EasyTier was developed by IBM research and monitors sub-LUN pieces (extents) and puts hot extents on SSD with the rest on SATA. The extent size 16MB to 8GB and is settable, with the default being 256MB. The system learns over time as it watches the data patterns; it's autonomic."
As they say, "this is not your father's disk drive".
A LUN, by the way, is a Logical Unit Number, and has to do with sub-dividing these modern gigantic pools of storage into smaller units.