Try a better solution. Netbackup is predicated on filenames and is not suited to be used for backing up millions of small files through regular netbackup means even if using multistreaming. Please read this technote.
DOCUMENTATION: How to configure backup for maximum throughput when a volume or folder contains millions of small files.
When a volume contains millions of small files, backup throughput may commonly drop below 1MB/sec. This is normal behavior due to the overhead of file requests that must be made to the operating system.
In this scenario, FlashBackup is recommended for maximum throughput while maintaining the ability to restore individual files.
If FlashBackup is not an option, a Windows 2000 client with VERITAS Snapshot Provider (VSP) (or Windows 2003 with VSP or Volume Shadow copy service (VSS)) can be configured to perform raw partition backups using a snapshot. This will allow the volume to be accessed while a backup is running, but give the performance of a raw partition backup.
However, there is no ability to restore individual files. In order to restore individual files from this volume, the entire volume must be restored, and then the files can be copied to where they are needed. The restore can also be redirected to a new or blank volume that is available for overwrite by the restore. The assumption is that due to the number and type of files, these files are likely to only be restored in a disaster recovery situation.
...and there is more info if you follow the link you can read the entire technote.
