upgrade from 7.1 to 7.5.0.6

I think the repeated lesson from many posts on this forum, is to check the compatilibity lists.

My advice is to find out the version of everything in your environment before doing anything else... masters, medias, clients, both NetBackup and OS (and OS patch levels) - and the hardware models, and hardware firmware versions and the versions of any specific software directly related to the hardware/storage (e.g. OST versions etc, e.g. DD boost versions) - and then, for each and every combination of OS, NBU, storage - to go through *all* of the NetBackup compatibility lists (SCL, DB SCL, HCL, VM) - slowly, carefully, and thoroughly.

As reveraoo suggests, use SORT - it does the above (mostly) for you.  So, let SORT check most of it for you, and then any low level details can be checked by you and your team.

The above is your research stage.

You need to know your environment, in detail, before you can begin planning.

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Ever heard the expression of "The Five P's" ?

Proper Planning Prevents Poor Performance.