ZFS is used by PVE if you want some software RAID. You select the RAID level and which disks should be part of it. The free space is shared among the datasets (root file system, guest storage, ISOs, ...). You can also use multiple pools if you like to split it up a bit by only selecting the disks for the system during installation and once the system is up, create another pool with the remaining disks.
How many disks do you have? Did you consider having some redundancy so that the failure of a single disk will not bring down the whole server?