>Hi Richard, what about migrations. When you migrate data from one pool to
>the next, does migration reconstruct aggregates of empty space???

Hi, Mark.  Good question.  From all that I know, only the Reclamation
process goes inside Aggregates to reclaim empty space therein.
Storage pool migration, storage pool backup/restore, and move data operations
have to operate at high speed and can't afford to do anything more than
move Aggregates as-is.  One of the reasons for Small Files Aggregation was
to enhance the performance of those operations, to operate on larger bundles
of data.  (See ADSMv3 Technical Guide, p.94.)
  Richard