Hi,
it could be that ZFS just reports a lower value because of compression (you can check with
zfs get all path/to/your/subvol | grep compress
) or there could also be sparse files. But please note that the PBS storage usage is not at all the sum of those sizes, it also has compression and also deduplication:
https://pbs.proxmox.com/docs/introduction.html#main-features See the
Deduplication Factor
in your Datastore summary