NetBSD 6.1 filesystem notes.

The filesystem must be not mounted

root@farnsworth ~ # umount /disks/disk1
root@farnsworth ~ # umount /disks/disk2
root@farnsworth ~ # file -s /dev/wd1a
/dev/wd1a: Unix Fast File system [v1] (little-endian), last mounted on /disks/disk1, last written at Tue Jul 16 09:38:49 2013, clean flag 1, number of blocks 122096646, number of data blocks 121138363, number of cylinder groups 644, block size 32768, fragment size 4096, minimum percentage of free blocks 5, rotational delay 0ms, disk rotational speed 60rps, TIME optimization
root@farnsworth ~ # file -s /dev/wd2e
/dev/wd2e: Unix Fast File system [v1] (little-endian), last mounted on /disks/disk2, last written at Sat Jul 20 02:00:58 2013, clean flag 1, number of blocks 78142160, number of data blocks 77529094, number of cylinder groups 412, block size 32768, fragment size 4096, minimum percentage of free blocks 5, rotational delay 0ms, disk rotational speed 60rps, TIME optimization
root@farnsworth ~ #

Also you can do it with dumpfs:

root@farnsworth ~ # dumpfs -s /dev/wd1a
file system: /dev/rwd1a
format  FFSv1
endian  little-endian
magic   11954           time    Sat Jul 20 02:21:25 2013
superblock location     8192    id      [ 51e514a9 69cdbabc ]
cylgrp  dynamic inodes  4.4BSD  sblock  FFSv2   fslevel 4
nbfree  15140244        ndir    1       nifree  30334972        nffree  18
ncg     644     size    122096646       blocks  121138363
bsize   32768   shift   15      mask    0xffff8000
fsize   4096    shift   12      mask    0xfffff000
frag    8       shift   3       fsbtodb 3
bpg     23699   fpg     189592  ipg     47104
minfree 5%      optim   time    maxcontig 2     maxbpg  8192
symlinklen 60   contigsumsize 2
maxfilesize 0x004002001005ffff
nindir  8192    inopb   256
avgfilesize 16384       avgfpdir 64
sblkno  8       cblkno  16      iblkno  24      dblkno  1496
sbsize  4096    cgsize  32768
csaddr  1496    cssize  12288
cgrotor 0       fmod    0       ronly   0       clean   0x02
wapbl version 0x1       location 2      flags 0x0
wapbl loc0 488401024    loc1 131072     loc2 512        loc3 3
flags   wapbl
fsmnt   /disks/disk1
volname         swuid   0

Differences between FFSv1 and FFSv2

From newfs man page -O option:

0    4.3BSD; This option is primarily used to build root file systems that can be understood by older boot ROMs.  This generates an FFSv1 file system with level 1 format.
1    FFSv1; normal Fast File System, level 4 format. Also known as `FFS', `UFS', or `UFS1'.  This is the default.
2    FFSv2; enhanced Fast File System, suited for more than 1 Terabyte capacity.  This is also known as `UFS2'.

from fsck_ffs man page:

FFS1 level 0 = inode 4.2/4.3BSD static table
FFS1 level 1 = dynamic table
FFS1 level 2 = 32bit UID/GID, compact symlinks
FFS1 level 3 = free segment maps
FFS1 level 4 = FFS2 style superblock (allows WAPBL)
FFS2 level 5 = 64bit addresses, 64bit timestamps, birthtime, ext attributes 

FFSv2 is suitable for large disk (1TB)

Here is example how to change default percentage of disk space held back from normal users to 1%. Default is 5% and this is too much for large disks.

root@farnsworth ~ # tunefs -m 1 /dev/wd1a
tunefs: tuning /dev/rwd1a
tunefs: minimum percentage of free space changes from 5% to 1%
tunefs: should optimize for space with minfree < 5%