(((Thanks to those that have answered my 3480->3490 questions.)))

On the topic of migration:

I always wondered what good it would be to have a low migration number that
is other than zero for DASD storage, especially when you have caching on, and
I stumbled across a good reason.

It says in the manual that the low migration number will determine whose
data is *not* put to tape.  It does this by virtue of the
fact that it first writes to tape the user with the largest amount of
data, therefore small users tend to accumulate below the low threshold
number until they are considered greater than everyone else there with them.
At some point they become a large-amount-of-data user and have their tape
mounted for writing.

If you have COLLOCATION ON then this can also help
minimize how often a tape is mounted to put 1 users data on it!

                  Got that?
                           cheers ... joe.f.