> Jan 23 13:27:38 neptune /netbsd: sd0: 1440 KB, 80 cyl, 2 head, 18 sec, 512 bytes/sect x 2880 sectors
> Jan 23 13:27:58 neptune /netbsd: sd0: dos partition I/O error
> Jan 23 13:28:48 neptune /netbsd: sd0: dos partition I/O error
>
> The "dos partition I/O errors" are in response to my attempts to mount a
> DOS-formatted floppy.  I've tried /dev/sd0a through /dev/sd0d (the latter
> being what I used to use when this was working in previous versions).  I've
> also tried formatting the disk and writing characters to it.  All fail
> with:
>
> % newfs_msdos /dev/rsd0d
> /dev/rsd0d: 2840 sectors in 355 FAT12 clusters (4096 bytes/cluster)
> MBR type: 1
> bps=512 spc=8 res=1 nft=2 rde=512 sec=2880 mid=0xf0 spf=2 spt=18 hds=2 hid=0
> newfs_msdos: /dev/rsd0d: Input/output error
>

try first

disklabel sd0


and see that dos partition is sd0e...

(but possibly it's error anyway)