Peter,

I presume that the old storage pool & the new storage pool both have
different copy storage pools?

If this is the case then a backup storage pool of the new storage pool
to it's corresponding copy storage pool will copy everything from the
new primary to the new copy.

In this case what is left in the old copy storage pool is no longer
required as it is duplicated in the new copy storage pool.  In effect
you will have two copies!  You can safely delete the old copy storage
pool volumes in this case.

I think the explanation is that the backup storage pool command copies
all data in the primary to the copy, that is not already found in the
copy.  Fullstop.  It does not reconcile the two completely.  I presume
this is to cater for the case where you may delete a primary volume for
some reason (maybe damaged) and then want to use the copy to recover
the primary.  If it did a reconcile then it could be disastrous if a
backup storage pool command was run before the recover could be
completed.

Cheers,
Simon