UFS gmirror raid1 + bare bsdlabel (no mbr)


I'm trying to follow handbook instructions (chapter 18.3.3) on setting up a software RAID1 between an existing installation on SSD da6 to a same model/capacity SSD da7. Actually, da6 is using bare BSD Label partition scheme without MBR (I know, I know...). What I did so far:

# sysctl kern.geom.debugflags=16
kern.geom.debugflags: 0 -> 16

# diskinfo -v da6 | head -n3
        512             # sectorsize
        120034123776    # mediasize in bytes (112G)

# geom zero load

# gnop create -s 120034123776 gzero

 # gmirror label -v gm0 gzero.nop da7
Metadata value stored on gzero.nop.
Metadata value stored on da7.

# gmirror forget gm0

# gpart show da6
=>        0  234441648  da6  BSD  (112G)
          0  226492416    1  freebsd-ufs  (108G)
  226492416    7949231    2  freebsd-swap  (3.8G)
  234441647          1       - free -  (512B)

I'm a little confused about how to proceed from this point. I'm not sure how I should do the partitions backup/restore since my partition scheme differs from the guide.

Any help would be very appreciated. Thanks in advance!
Now I understand why it's called "dangerously dedicated" layout. Is there any way to do this keeping this layout or maybe converting it to MBR without data loss?
No, sorry. Backup, repartition, restore.

Thanks for your fast response, wblock!

I managed to backup, reinstall the system, restore. Following the instructions now I'm stuck with this error when trying the dump/restore procedure:

# mount /dev/mirror/gm0s1a /mnt
# dump -C16 -b64 -0aL -f - /    | (cd /mnt && restore -rf -)
mksnap_ffs: Cannot create snapshot //.snap/dump_snapshot: /: Snapshots are not yet supported when running with journaled soft updates: Operation not supported
dump: Cannot create //.snap/dump_snapshot: No such file or directory

Tape is not a dump tape
Use tunefs(8) to disable Soft Updates Journaling on that filesystem. This has to be done when it is not mounted:
tunefs -j disable /dev/mirror/gm0s1a

Since there is no data on that filesystem, you can just reformat it. The Handbook instructions use newfs -U to avoid SUJ.
wblock@, I did the format process using newfs -U as per instructions. May it be because I used -t switch together to enable trim, since it's a SSD? I need to enable trim on disks and mirror/gm0 or just on the disks? What's the best practice in this case? Thanks again!
I don't understand the question. -U is for soft updates, which is fine. The journaling part is only enabled if -j is added. I don't use SUJ, and don't recommend it.

That has nothing to do with trim. Trim is a UFS property, so it can only be enabled on a UFS filesystem, not on the mirror device.