Wow! Thanks for all the responses.  I am replying to this e-mail because it
actually is the one that gave the most detailed explanation.

Many of you reminded me that the directory structures go to the management
class with the longest retention.  In our case both have exactly the same
retention and that was what was throwing me for a loop.  It appears (as
noted far below) that when two classes have the same retention settings, it
is unpredictable which one the directory structures will get bound to.

At one site we have 2 very large machines that we want to go to tape.  We
only want these 2 clients to go to tape.  We have 2 tape drives and while
they are backing up to tape both drives are busy.  So when another client
that should go to disk comes along it still waits for the media to become
available so it can save its directory structure there.

At another site we have 2 tape pools.  In one pool we want to store the data
of cad clients for a longer period of time.  In the other pool we want to
store all the other client data.  Our intent was to have 2 pools each
associated with a specific group of clients.  What we got was one with all
the cad data and cad directory structures along with the directory
structures from all the other clients.  The other only had the data from the
other clients.

In both cases I believe our solution is to create another Policy Domain.  We
will make sure that each has only one management class within its respective
Policy Set.  Then by adding the node to the correct Domain everything should
work as we want it to.

Last, I did realize that the dirmc command would force the directory
structures to a specific place.  This option while useful could also be
dangerous.  If in the future I create another management class with a longer
retention I would have to remember to go back to the dirmc and alter what
class it points to.  If I am the administrator forever no problem (yea
right) but as time goes on and people change I fear one day we might have
directory structures going to a class with a shorter retention period than
the data.

Again, Thanks for all the great and helpful responses.

Kyle