ILM, for those new to IT storage, was and still is the process of identifying old data and then moving that data to a SATA-based storage system or tape. Ironically, we saw in the past the same percentage of inactive data as we do now (around 80 percent), but the problem was that most data centers already had overbought storage to the point that they had plenty of excess space anyway.
The economics didn't make sense. If you had 20 TBs of storage and were only using 10 TBs of it, the fact that we could identify that 8 TBs of that storage was old and should be stored somewhere else didn't matter. Paying for an additional 8+ TBs of additional storage when you already had 10 TBs of free space didn't make sense, even if that tier was cheaper by the gigabyte.
In 2009, we're going to have a different scenario. More data centers are at a much higher level of capacity utilization, and that 80 percent of data that is old has gone up a little bit. Some surveys now point to 90 percent. And Primary Storage Optimization is more than just moving old data off of primary storage -- it also includes better optimization of data on primary storage that is not moved.
The first big difference between PSO and ILM is that PSO has a better target to move to than has been available in the past: disk-based archives. Designed to optimize capacity, to scale, and to simplify management, these systems are a significant step ahead of what the target tier in 2001 was.