Snapshot creation fails with error 156
Snapshot creation fails when multiple volumes are mounted to the same mount point. Consider a scenario where /vol/gvol1 and /vol/gvol2 are mounted on /mnt. Here the volumes gvol1 and gvol2 are both mounted on the same mount point /mnt. When a backup policy is run to take snapshot backups, the snapshot creation fails with error 156 as both the volumes are mounted on the same mount point.
The reason for snapshot creation failure in the above case is that there would be multiple entries in OS mount table for the same mount point, which is an unsupported configuration in NetBackup.
Veritas recommends that you mount each volume on separate mount points.
Snapshot creation can fail due to multiple reasons. The reason mentioned above is just one of them.