For various reasons, sometimes it is useful for a hypervisor to access data served by a virtualized guest system. In this example, it's Proxmox accessing NFS shares on a TrueNAS virtual machine. TrueNAS could just as easily be replaced with Openmediavault or any other NAS server, but the concept of recursive storage access remains the same. NFS in this example could also be replaced with iSCSI, or even SMB.