I'm not sure that the above answers my question exactly of course I could be having a "slow" day.

Data Deduplication is much like single instance messaging but for files sometimes referred to as intelligent compression or single instance storage. This can track and index bit/level, block/level changes and applies one or more algorithms to detect changes so only the delta to for a file is captured rather than an entire new file being saved.

The other question is more about file management and if I can Define one presented storage group (VG i think in the product terminology) The VG would be made up of 1 or more raid set for the total space.

VolumeGroup0
DiskGroup0 Raid10 with 24x73GB 15K RPM drives
DiskGroup1 Raid5 with 5x500GB 7200RPM drives

In this case a total of 2.8TB will be available but "active" files would reside on the raid10 and inactive files would be moved to the slower raid5.

*alternatlivly DiskGroup1 could "virtual" as in a volume to which data is replicated to from unit1 to a VG on unit2 while any references to files moved based on the ageing algorithm would redirect the client the file located on unit2.

This gets more into data lifecycle management but an addition of something like this, even if a simple implimentation, would drastically increase the value of the product.