PBS with different discs

I need to install PBS on a server with these 4 HDDs: 2TB, 2TB, 1TB, 500GB

I plan to use 2x2TB in ZFS RAID1 as S.O. and VM datastore and I would like to have some suggestions on how to use the other disks (perhaps I could dedicate the 1TB one to archiving files sent by "proxmox-backup-client"?)

Thanks for any advice