We are doing this (same disk primary pool backed to two different tape
copy pools):

  parallel
  backup stg criticaldp criticaltc maxpr=1 wait=yes
  backup stg criticaldp backupcopy maxpr=1 wait=yes

It results in:

     143 Backup Storage Pool  Primary Pool CRITICALDP, Copy Pool
CRITICALTC,
                               Files Backed Up: 2059, Bytes Backed Up:
                               66,581,766,144, Unreadable Files: 0,
Unreadable
                               Bytes: 0. Current Physical File
(bytes):
                               5,568,978,944 Current output volume:
AU0217.
     144 Backup Storage Pool  Primary Pool CRITICALDP, Copy Pool
BACKUPCOPY,
                               Files Backed Up: 2059, Bytes Backed Up:
                               66,581,766,144, Unreadable Files: 0,
Unreadable
                               Bytes: 0. Current Physical File
(bytes):
                               5,568,978,944 Current output volume:
AU0304.

It looks like TSM is smart enough to read the file from disk once, and
write to tape twice.

Does anyone know if this is the case and if/where it is documented?