Resolvido por isso:
name = 'ArkOS_Dev'
kernel = "/mnt/arch/boot/x86_64/vmlinuz"
ramdisk = "/mnt/arch/boot/x86_64/archiso.img"
extra = "archisobasedir=arch archisolabel=ARCH_201511"
memory = 2048
vcpus = 3
disk = [ "format=raw, vdev=xvda, access=rw, target=/dev/vm_volumes/root.ArkOS_Dev",
"format=raw, vdev=xvdb, access=rw, target=/dev/vm_volumes/swap.ArkOS_Dev",
"format=raw, vdev=xvdc, access=ro, devtype=cdrom, target=/home/xen/ISO/archlinux-2015.11.01-dual.iso"
]
vif = [ 'mac=00:16:3e:49:2b:a1,bridge=xenbr0' ]
root = "/dev/xvda rw"
Depois de instalar o DomU com isto:
name = 'ArkOS_Dev'
bootloader = "pygrub"
memory = 2048
vcpus = 3
disk = [ "format=raw, vdev=xvda, access=rw, target=/dev/vm_volumes/root.ArkOS_Dev",
"format=raw, vdev=xvdb, access=rw, target=/dev/vm_volumes/swap.ArkOS_Dev"
]
vif = [ 'mac=00:16:3e:49:2b:a1,bridge=xenbr0' ]
root = "/dev/xvda rw"