There are a bunch of files on the floppy when mounted; I delete them all; but then, there is a large amount of 'used' space! unmounting + remounting 'fixes' this problem.
# mount_msdos /dev/sd2a /a
# ls -l /a
total 2
drwxr-xr-x 1 root wheel 512 Jan 4 13:11 System Volume Information/
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.0*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.1*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.10*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.11*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.12*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.13*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.14*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.15*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.16*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.17*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.18*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.19*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.2*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.20*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:22 six.21*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.3*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.4*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.5*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.6*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.7*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.8*
-rwxr-xr-x 1 root wheel 65536 Jan 4 21:21 six.9*
-rwxr-xr-x 1 root wheel 275 Jan 4 21:22 six.bat*
# df -h /a
Filesystem Size Used Avail %Cap Mounted on
/dev/sd2a 1.4M 1.4M 14K 99% /a
# rm -rf /a/*
zsh: sure you want to delete all 24 files in /a [yn]? y
# ls -l /a
# df -h /a
Filesystem Size Used Avail %Cap Mounted on
/dev/sd2a 1.4M 517K 907K 36% /a
# umount /a
# mount_msdos /dev/sd2a /a
# ls -l /a
# df -h /a
Filesystem Size Used Avail %Cap Mounted on
/dev/sd2a 1.4M 17K 1.4M 1% /a