@pfr 
Formatting a 16GB usb to FFSv2 on NetBSD, just follow Chapter 13.
Does this make any sense to you?? If not, don't worry, it will sooner or later 🙂
pin@mybox $ sysctl hw.disknames
hw.disknames = wd0 sd0
pin@mybox $ doas dd if=/dev/zero of=/dev/sd0 bs=1m count=1
Password:
1+0 records in
1+0 records out
1048576 bytes transferred in 0.689 secs (1521880 bytes/sec)
pin@mybox $ doas fdisk -au sd0
Password:
fdisk: primary partition table invalid, no magic in sector 0
fdisk: Cannot determine the number of heads
Disk: /dev/rsd0
NetBSD disklabel disk geometry:
cylinders: 14784, heads: 64, sectors/track: 32 (2048 sectors/cylinder)
total sectors: 30277632, bytes/sector: 512
BIOS disk geometry:
cylinders: 1023, heads: 255, sectors/track: 63 (16065 sectors/cylinder)
total sectors: 30277632
Partitions aligned to 16065 sector boundaries, offset 63
Do you want to change our idea of what BIOS thinks? [n] 
Partition table:
0: <UNUSED>
1: <UNUSED>
2: <UNUSED>
3: <UNUSED>
Bootselector disabled.
No active partition.
Drive serial number: 0 (0x00000000)
Which partition do you want to change?: [none] 0
The data for partition 0 is:
<UNUSED>
sysid: [0..255 default: 169] 
start: [0..1885cyl default: 63, 0cyl, 0MB] 
size: [0..1885cyl default: 30277569, 1885cyl, 14784MB] 
bootmenu: [] (space to clear) 
Partition table:
0: NetBSD (sysid 169)
    start 63, size 30277569 (14784 MB, Cyls 0-1884/177/21)
        PBR is not bootable: All bytes are identical (0x00)
1: <UNUSED>
2: <UNUSED>
3: <UNUSED>
Bootselector disabled.
No active partition.
Drive serial number: 0 (0x00000000)
Which partition do you want to change?: [none]
Do you want to change the active partition? [n]
We haven't written the MBR back to disk yet. This is your last chance.
Partition table:
0: NetBSD (sysid 169)
    start 63, size 30277569 (14784 MB, Cyls 0-1884/177/21)
        PBR is not bootable: All bytes are identical (0x00)
1: <UNUSED>
2: <UNUSED>
3: <UNUSED>
Bootselector disabled.
No active partition.
Drive serial number: 0 (0x00000000)
Should we write new partition table? [n] y
pin@mybox $ doas disklabel sd0
Password:
# /dev/rsd0:
type: SCSI
disk: DataTraveler 3.0
label: fictitious
flags: removable
bytes/sector: 512
sectors/track: 32
tracks/cylinder: 64
sectors/cylinder: 2048
cylinders: 14784
total sectors: 30277632
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0 
5 partitions:
#        size    offset     fstype [fsize >
 c:  30277569        63     unused      0 >
 d:  30277632         0     unused      0 >
 e:  30277569        63     4.2BSD      0 >
disklabel: boot block size 0
disklabel: super block size 0
pin@mybox $ doas newfs -O 2 /dev/rsd0e
Password:
/dev/rsd0e: 14784.0MB (30277568 sectors) block size 16384, fragment size 2048
        using 80 cylinder groups of 184.81MB, 11828 blks, 22976 inodes.
super-block backups (for fsck_ffs -b #) at:
160, 378656, 757152, 1135648, 1514144, 1892640, 2271136, 2649632, 3028128,
..............................................................................
pin@mybox $ sysctl hw.disknames
hw.disknames = wd0 sd0
pin@mybox $ doas mount /dev/sd0e /home/pin/Extmedia/                                                                                                                   
Password:
pin@mybox $ df -h
Filesystem         Size       Used      Avail %Cap Mounted on
/dev/wd0a          2.8G       173M       2.5G   6% /
/dev/wd0f          1.9G        96M       1.7G   5% /var
/dev/wd0e           17G       5.2G        11G  32% /usr
/dev/wd0g          3.8G       113M       3.5G   3% /home
kernfs             1.0K       1.0K         0B 100% /kern
ptyfs              1.0K       1.0K         0B 100% /dev/pts
procfs             4.0K       4.0K         0B 100% /proc
tmpfs              1.9G         0B       1.9G   0% /var/shm
/dev/sd0e           14G       2.0K        13G   0% /home/pin/Extmedia
pin@mybox $ doas umount /dev/sd0e
Password:
pin@mybox $ df -h
Filesystem         Size       Used      Avail %Cap Mounted on
/dev/wd0a          2.8G       173M       2.5G   6% /
/dev/wd0f          1.9G        96M       1.7G   5% /var
/dev/wd0e           17G       5.2G        11G  32% /usr
/dev/wd0g          3.8G       113M       3.5G   3% /home
kernfs             1.0K       1.0K         0B 100% /kern
ptyfs              1.0K       1.0K         0B 100% /dev/pts
procfs             4.0K       4.0K         0B 100% /proc
tmpfs              1.9G         0B       1.9G   0% /var/shm
No errors on mounting or unmounting the drive. Obviously, if you want to share the drive with another machine running another OS you should not format it to FFSv2 😉
Check the output of fdisk -l for the options of file systems and man newfs for the flags and options before writing the partitions to disk.