We are running ADSM Version 1 under AIX with 3490E cartridge drives.

Once a week we run an EXPORT NODE operation including all active backup
files for four nodes to generate tapes for offsite vaulting. This uses
about sixty volumes and takes about a day. We recently had to rerun
the EXPORT NODE operation after a failure, and ended up with a client
attempting to back up a very large file while the rerun was in progress.
The client backup failed because the file size was such that it was
supposed to go directly to out tape storage pool, and the EXPORT was using
both of the tape drives we had installed at the time (one for its output
tapes and one for the various tape storage pool volumes containing active
backup files).

We subsequently installed a third tape drive. EXPORT NODE operations now
use all three tape drives. They still use one drive for output tapes,
but they spread the storage pool tape mounts across the other two drives.
Does anyone know what would happen if the situation described above
arose now? Would EXPORT NODE hog all three drives and force a failure
of the client backup operation? More generally, where are the rules
governing ADSM's allocation of devices to different tasks documented?