Cause 1: Check the space usage of the storage units.
Log in to the NetBackup Administration Console as the root user. Choose NetBackup Management > Storage > Storage Units to view the space usage of the storage units.
If the space usage reaches 100% or a specific level, you must release certain storage space or create a larger storage unit and add the storage unit to the storage unit group.
Cause 2: Adjust the number of backup task attempts.
1. On the NetBackup Administration Console, choose NetBackup Management > Host Properties > Master Servers. Right-click the master server name and select Properties.
2. Select Global Attributes. Set the value of Schedule backup attempts > _tries to be larger than the number of storage units in the storage unit group. The default value is 2 and the maximum value is 32.
Cause 3: Perform the backup task again after restarting the NetBackup service.
1. The available space of the storage unit group cannot satisfy the backup requirement.
2. The number of backup task attempts is small and the number of backup task attempts reaches the upper limit before an available storage unit is found.
3. A history record for backup task failure due to insufficient disk space for the storage unit group exists.