Migrate UFS drive from FreeNAS to DragonFly BSD

I'm trying to migrate my home server from FreeNAS 8.3 to DragonFly BSD. In order to shuffle my files about I picked up a Seagate 8Tb Archive disk, attached it via eSATA, formatted it as UFS under FreeNAS then patiently waited about a week for it to trickle full. Now I've got DragonFly going, but try as I might I can't get the UFS volume mounted. Is there some way to get this thing mounted under DragonFly? I can see that the drive is using GPT (and a protective MBR) and is definitely UFS. Is there something incompatible between the two systems, despite their FreeBSD heritage? It also seems odd that I can see slices but not partitions. I expected ls /dev/ad6* to give me something like /dev/ad6p1a since the drive is using GPT, but evidently not. I'm yet to try anything invasive (as in, write to the disk) because I'm completely in the dark on what the cause is. % uname -a DragonFly loki.misque.me 4.4-RELEASE DragonFly v4.4.3-RELEASE #5: Mon Apr 18 22:47:32 EDT 2016 root@www.shiningsilence.com:/usr/obj/home/justin/release/4_4/sys/X86_64_GENERIC x86_64 Some basic information about the disk: % ls /dev/ad6* /dev/ad6 /dev/ad6s0 /dev/ad6s1 % cat /etc/fstab # Device Mountpoint FStype Options Dump Pass# /dev/serno/4C530012740115112064.s1a / ufs rw 1 1 /dev/serno/4C530012740115112064.s1d /home ufs rw 2 2 /dev/serno/4C530012740115112064.s1e /tmp ufs rw 2 2 /dev/serno/4C530012740115112064.s1f /usr ufs rw 2 2 /dev/serno/4C530012740115112064.s1g /var ufs rw 2 2 /dev/serno/4C530012740115112064.s1b none swap sw 0 0 proc /proc procfs rw 0 0 /dev/ad6s1 /mnt/backup ufs ro 0 0 The mount effort in question: % sudo mount -v /mnt/backup mount_ufs: /dev/ad6s1 on /mnt/backup: incorrect super block And my diagnostic efforts: % sudo fdisk /dev/ad6 ******* Working on device /dev/ad6 ******* parameters extracted from device are: cylinders=15504021 heads=16 sectors/track=63 (1008 blks/cyl) Figures below won't work with BIOS for partitions not in cyl 1 parameters to be used for BIOS calculations are: cylinders=15504021 heads=16 sectors/track=63 (1008 blks/cyl) Media sector size is 512 Warning: BIOS sector numbering starts with sector 1 Information from DOS bootblock is: The data for partition 1 is: sysid 238,(EFI GPT) start 1, size 4294967295 (2097151 Meg), flag 80 (active) beg: cyl 0/ head 0/ sector 2; end: cyl 1023/ head 255/ sector 63 The data for partition 2 is: The data for partition 3 is: The data for partition 4 is: % sudo disklabel64 -r ad6 disklabel64: bad pack magic number % sudo disklabel64 -r ad6s0 disklabel64: bad pack magic number % sudo disklabel64 -r ad6s1 disklabel64: bad pack magic number % sudo camcontrol devlist at scbus3 target 1 lun 0 (da0,sg0,pass0) at scbus3 target 2 lun 0 (da1,sg1,pass1) at scbus3 target 3 lun 0 (da2,sg2,pass2) at scbus3 target 4 lun 0 (da3,sg3,pass3) at scbus3 target 5 lun 0 (da4,sg4,pass4) at scbus3 target 6 lun 0 (da5,sg5,pass5) at scbus3 target 7 lun 0 (da6,sg6,pass6) at scbus6 target 0 lun 0 (pass8,sg8,da8) % sudo gpt show /dev/ad6 start size index contents 0 1 - PMBR 1 1 - Pri GPT header 2 32 - Pri GPT table 34 94 - 128 4194304 0 GPT part - FreeBSD Swap 4194432 15623858696 1 GPT part - FreeBSD UFS/UFS2 15628053128 7 - 15628053135 32 - Sec GPT table 15628053167 1 - Sec GPT header % sudo file -s /dev/ad6 /dev/ad6: DOS/MBR boot sector; partition 1 : ID=0xee, active, start-CHS (0x0,0,2), end-CHS (0x3ff,255,63), startsector 1, 4294967295 sectors % sudo file -s /dev/ad6s1 /dev/ad6s1: Unix Fast File system [v2] (little-endian) last written at Thu Jan 1 00:00:00 1970, number of blocks 0, number of data blocks 0, pending blocks to free 0, system-wide uuid 0,