Thanks guys for your help.
I had started a new post as I needed to know if there was an official supported procedure for storage change/switch.
between your suggestions and the other post, finally I got the result I wanted.
basically, a copy of the structure to new HD is the final solution.
Few consideration before doing that are needed:
A simple clone would not work as the new disk is bigger than 2TB. MBR dont work.
So you need to create a partition table on GPT.
Than copying files is longer and more risky. A clone disk-to-disk is better.
Finally Clonezilla with a small change in advanced option is the final solution.
Details I have written in my other post:
https://help.nextcloud.com/t/offial-procedure-to-substiture-external-storage/80339/9
I hope this will help others on same situation.
Thanks again