We all know that you shouldn't back up a client to a Media Server of a lower version of NetBackup but sometimes it is easy to make an oversight.
An example cropped up recently for me at a straight forward staged upgrade.
The plan was a Master Server upgrade in week 1, let that settle for a couple of weeks before upgrading the Media Servers then a couple more weeks and upgrade all clients - change control / rollback options and all that!
Along the way it was decided to virtualise the Master Server too.
Sounded OK until we did the testing when everything worked great apart from the Catalog backup which went to a Media Server (The Master being virtualised could not have tape drives)
The backup failed with a 154 - Storage Unit is not compatible - storage unit characteristics mismatched to request.
Couldn't find any tech notes and the penny hadn't quite dropped when I first saw the...