A new feature introduced in NetBackup 7.1 can cause NDMP backup failures. The Append-Only Mode described in this Symantec Tech Note causes the drive to prevent the overwrite of data on a cartridge unless the writing application performs a pre-authorization for the overwrite. This feature is supported on IBM LTO-5 drives with LTO-4 or LTO-5 media. The feature is enabled by default and does not normally cause any issues if all systems accessing the tape device are NetBackup 7.1 Media Servers.
In an NDMP environment, however, the storage device (filer, data mover) writes directly to the tape drives and may not be aware of the pre-authorization requirement. If these drives are shared between the NDMP device and the Netbackup Media Server, write errors occur, represented by a write protect message issued by the NDMP device. This has been observed with an EMC VNX array and EMC support was previously unaware of the Append-Mode feature.
The solution to the problem is to disable Append-Only mode by touching the <InstallPath>NetbackupdbconfigDISABLE_APPEND_MODE on the Netbackup Master Server and restarting the NetBackup Services.