This is a plan-ahead issue.  Nodes which need special handling like
that need to be assigned their own storage pool, where your site
should have distinct management classes for data having differing
requirements.  You can define such a storage pool, create a management
class & copy group pointing to it, and define a management class for
the node to use henceforth.  The MOVe NODEdata command can be employed
to shift existing data to that separate storage pool, whereafter the
desired Backup Stgpool operation can be performed.

If the data is static (no new incoming files), another approach could
be to define a new stgpool at the bottom of the current storage pool
hierarchy, with no migration into it, then MOVe NODEdata into that
pool, and do a Backup Stgpool on it.  This would avoid the need for a
new management class (though you should still pursue that).

   Richard Sims