I get many I/O errors when I try to newfs and use a floppy.
I tried this incantation:

# newfs -Tfloppy3 -i4096 -c 80 /dev/fd0a
newfs: /dev/fd0a: not a character-special device
/dev/fd0a:      2880 sectors in 80 cylinders of 2 tracks, 18 sectors
        1.4MB in 1 cyl groups (80 c/g, 1.41MB/g, 352 i/g)
super-block backups (for fsck -b #) at:
 32,
#

So that seemed OK.  But then copies to the disk elicited large
numbers of errors like this:

fd0: write failed st0 40<abnrml> st1 4<sec_not_fnd> st2 0 cyl 0 head 0 sec 17
blkno 16 skip 0 cylin 0 status 40
fd0: write failed st0 40<abnrml> st1 4<sec_not_fnd> st2 0 cyl 0 head 0 sec 17
blkno 16 skip 0 cylin 0 status 40
fd0: write failed st0 40<abnrml> st1 4<sec_not_fnd> st2 0 cyl 0 head 0 sec 17
blkno 16 skip 0 cylin 0 status 40
fd0a: hard error writing fsbn 16 of 16-18 (st0 40<abnrml> st1 4<sec_not_fnd> st2 0 cyl 0 hd 0 sec 17)
fd0: write failed st0 40<abnrml> st1 4<sec_not_fnd> st2 0 cyl 4 head 0 sec 1

It would appear that sectors 1 and 17 sure ought to be there...DOS
format and newfs don't complain...what to look for next?

BTW disklabel -r gives (the type=unknown is the only thing that looks
suspicious):

woodside# disklabel -r /dev/fd0a
# /dev/fd0a:
type: unknown
disk: floppy
label: 
flags:
bytes/sector: 512
sectors/track: 18
tracks/cylinder: 2
sectors/cylinder: 36
cylinders: 80
rpm: 300
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # milliseconds
track-to-track seek: 0  # milliseconds
drivedata: 0 

3 partitions:
#        size   offset    fstype   [fsize bsize   cpg]
  a:     2880        0    4.2BSD      512  4096    80   # (Cyl.    0 - 79)
  b:     2880        0    unused        0     0         # (Cyl.    0 - 79)
  c:     2880        0    unused        0     0         # (Cyl.    0 - 79)