Hi,
Ok, you said you're using NetBackup. Puredisk is a complete product on its onw that was purchased by Symantec but I'll not bore you with many details. It was the bought because of the deduplication feature which netbackup did not have. It was a completely seperate product back then (2008-2010 i think).
It could be use as a deduplicated storage pool with NetBackup (PDDO) or it could be used by itself. In many smaller remote sites it was used because it could be put there by itself to do the backups. It could then replicate these backups to a central site using deduplication , and thereby not using a lot bandwidth. Once the backup got to the central site it could then be exported to NetBackup tape media.
So that is the history. These days they have combined the product into NetBackup and you can now just use the netbackup clients in remote locations and backup to the central site and still use deduplication.
That is very high level but should give you a picture.