Disklabel for Mirrorset on HSG80

I have a mirrorset on two HSG80's.  I have it configured as folllows:

HSG BOTTOM>sho dev
Name          Type                      Port Targ  Lun        Used by
------------------------------------------------------------------------------
DISK10000     disk                         1    0    0        MIRR1
DISK10100     disk                         1    1    0
DISK10200     disk                         1    2    0
DISK20000     disk                         2    0    0        MIRR1
DISK20100     disk                         2    1    0
DISK20200     disk                         2    2    0

HSG BOTTOM>sho mirr
Name          Storageset                     Uses             Used by
------------------------------------------------------------------------------
MIRR1         mirrorset                      DISK10000        D0
                                             DISK20000

The disks in question are Model: BF0728A4BA disks from HP.  They have
72.8GB of space on them.  I did the following on my Tru64 4.0F server
to mount this raid:

$> disklabel -wr /dev/rrz16a
$> disklabel /dev/rrz16a
# /dev/rrz16a:
type: SCSI
disk: HSG80
label:
flags:
bytes/sector: 512
sectors/track: 255
tracks/cylinder: 4
sectors/cylinder: 1020
cylinders: 8369
sectors/unit: 142229253
rpm: 3600
interleave: 1
trackskew: 7
cylinderskew: 26
headswitch: 0           # milliseconds
track-to-track seek: 0  # milliseconds
drivedata: 0

8 partitions:
#          size     offset    fstype   [fsize bsize   cpg]      #
NOTE: values n                                      ot exact
  a:     131072          0    unused        0     0             #
(Cyl.    0 - 1                                      28*)
  b:     262144     131072    unused        0     0             #
(Cyl.  128*- 3                                      85*)
  c:  142229253          0    unused        0     0             #
(Cyl.    0 - 1                                      39440*)
  d:          0          0    unused        0     0             #
(Cyl.    0 - -                                      1)
  e:          0          0    unused        0     0             #
(Cyl.    0 - -                                      1)
  f:          0          0    unused        0     0             #
(Cyl.    0 - -                                      1)
  g:   70918018     393216    unused        0     0             #
(Cyl.  385*- 6                                      9912*)
  h:   70918019   71311234    unused        0     0             #
(Cyl. 69912*-                                       139440*)

I then did a newfs on partition 'c' to use the whole disk and mounted it:
$>df -k
Filesystem            Size  Used Avail Use% Mounted on
/dev/rz16c            68883207         1  61994885   1% /mnt

That shows roughly 66G gigs for size and only 59G available.  A far
cry from 72.8GB as labeled.  So, is it my disklabel that is screwed or
maybe a config on the HSG?  Or, is it that HP reports 72.8GB using
1000 1024K blocks as opposed to 1024 1024K blocks?  Also, why is the
partition size shown as 66G but only had 59G available.

Thanks,

fybar