Sorry for burring up this old post. I am pretty surprised that this issue does not arise more, but maybe most people don't use PBS to backup different customers.
Unlike namespaces, multiple datasets allow for different company specific settings. And it also show the storage usage of each customers, which you can't achive with namespaces.
So I was thinking about just creating multiple folders.
When using the web GUI to create a datastore, it seems to me like PBS creates a dataset and mount is to /mnt/datastore/name_of_your_pool.
So what worked in my testing, was to instead of using that datasets root (/mnt/datastore/name_of_your_pool),
I created the folders /mnt/datastore/name_of_your_pool/dataset1 and /mnt/datastore/name_of_your_pool/dataset2.
After that I created dataset1 with the absolute path /mnt/datastore/name_of_your_pool/dataset1 and dataset2 with the path /mnt/datastore/name_of_your_pool/dataset2
Unfortunatly I am not sure about any negative implications this could potentially have and if Proxmox supports using such a config.
it works, and supported , it's up to you : dedup will not effective between datastores/folders, while namespaces are required to keep whole datastore dedup.