Sounds like preemption process question.
I copied and pasted from TSM AIX 4.1 Manual. Refer to : Index, preemption
for more information.

Preemption of Client or Server Operations

The server can preempt server or client operations for a higher priority
operation when a mount point is in use and no others are
available, or access to a specific volume is required.

Mount Point Preemption

The following are high priority operations that can preempt operations for
a mount point:

     Backup database
     Restore
     Retrieve
     HSM recall
     Export
     Import

The following lists operations that can be preempted and are listed in
order of priority. The server selects the lowest priority operation
to preempt, for example reclamation.

   1.Move data
   2.Migration from disk to sequential media
   3.Backup, archive, or HSM migration
   4.Migration from sequential media to sequential media
   5.Reclamation

You can disable preemption by specifying NOPREEMPT in the server options
file. When this option is specified, the BACKUP DB
command is the only operation that can preempt other operations.

Volume Access Preemption

A high priority operation that requires access to a specific volume
currently in use by a low priority operation can automatically
preempt the operation. For example, if a restore request requires access to
a volume in use by a reclamation process and a drive is
available, the reclamation process is canceled and message ANR0494I or
ANR1441I is issued.

The following are high priority operations that can preempt operations for
access to a specific volume:

     Restore
     Retrieve
     HSM recall

The following lists operations that can be preempted, and are listed in
order of priority. The server preempts the lowest priority
operation, for example reclamation.

   1.Move data
   2.Migration from disk to sequential media
   3.Backup, archive, or HSM migration
   4.Migration from sequential media
   5.Reclamation

You can disable preemption by specifying NOPREEMPT in the server options
file. When this option is specified, no operation can
preempt another operation for access to a volume.


Sung Y. Lee
Enterprise Storage Services
Delivery Center - South, IBM Global Services
Office  (512) 823-1012 T/L:  793-1012
Fax      (512) 823-1037
Pager ( 800) 759-8888 PIN:  1087116
E-mail sunglee AT us.ibm DOT com



                      "Gill, Geoffrey
                      L."                      To:       ADSM-L AT VM.MARIST 
DOT EDU
                      <GEOFFREY.L.GILL@        cc:
                      SAIC.COM>                Subject:  tape mount priority
                      Sent by: "ADSM:
                      Dist Stor
                      Manager"
                      <[email protected]
                      .EDU>


                      07/22/2002 03:44
                      PM
                      Please respond to
                      "ADSM: Dist Stor
                      Manager"





Can anyone help me with what takes priority as it relates to tape drives?
If
all are in use for TSM's daily processes what can bump them? If all are in
use for a backup session what can bump them? Is this posted anywhere?

Thanks,
Geoff Gill
TSM Administrator
NT Systems Support Engineer
SAIC
E-Mail:    <mailto:gillg AT saic DOT com> gillg AT saic DOT com
Phone:  (858) 826-4062
Pager:   (877) 905-7154