newfs failure - only for read

["Boo Geum Jung" <bgjung%etri.re.kr@localhost>]

==========================
# disklabel sd0
# /dev/rsd0c:
type: unknown
disk: NetBSD
label:
flags:
bytes/sector: 512
sectors/track: 395
tracks/cylinder: 6
sectors/cylinder: 2370
cylinders: 15110
total sectors: 35843670
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

8 partitions:
#        size    offset     fstype  [fsize bsize cpg/sgs]
 a:  20174985       395     4.2BSD   1024  8192    16   # (Cyl.    0*-
8512*)
 b:    135090  20175380       swap                      # (Cyl. 8512*-
8569*)
 c:  35843275       395     unused      0     0         # (Cyl.    0*-
15123*)
 d:  35843670         0     unused      0     0         # (Cyl.    0 -
15123*)
 e:  15533200  20310470     4.2BSD   1024  8192    16   # (Cyl. 8569*-
15123*)
#
#
#
# newfs /dev/sd0
newfs: /dev/sd0c: open for read: Operation not supported by device
#
=======================

I'd like to di partition of sd0 with big root partition,
because "sysinst" can't make root partition big, I don't know why.
Anyway, I used "disklabel" command.
So I made sd0 just above.
But "newfs /dev/sd0a" complained it's read-only file system.
What's wrong with me?