No response from the OP in over 2 weeks?
We don't know which File type/manufacturer or if drives are shared between NAS filer and NBU media server(s).
If this is NetApp and drives are shared, check that SCSI Reserve/Release is configured on the filer.
Extract from NDMP Appliance Information: http://www.symantec.com/docs/TECH31885 :
Tips for control and configuration
■ For NDMP devices to share tape drives, tape reservation must be enabled in
the ONTAP software on the filer as well as in NetBackup. You can use either
SCSI persistent reservation or SCSI reservation. To share tape drives, note
that the drive itself must support one of these types of reservation.
To enable SCSI reservation in Data ONTAP, enter either of the following at the ONTAP command line on the filer:
options tape.reservations scsi
options tape.reservations persistent
To enable SCSI reservation in the NetBackup Administration Console, go to Host Properties > Media Servers > double click the media server > Properties > Media. Make sure to select the same type of SCSI reservation as you set on the filer.
