[CentOS] Wrong disk size problem.

Hi,we have Centos 5.4 server and according to me we have strange problem.

Disk size and other indormation like below.Normally,md2 partition
should have 46GB free disk size but available value is zero.Why it
show zero ? If you help me,I will be happy.

df -h

Filesystem            Size  Used Avail Use% Mounted on
/dev/md1               19G  2.1G   16G  12% /
/dev/md2              880G  834G   0  100% /data
/dev/md0              243M   24M  208M  11% /boot
tmpfs                 2.0G     0  2.0G   0% /dev/shm

df -k

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/md1              19840804   2215556  16601112  12% /
/dev/md2             922019416 874435436         0 100% /data
/dev/md0                248783     23904    212035  11% /boot
tmpfs                  2057656         0   2057656   0% /dev/shm


df -i

Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/md1             5124480   44654 5079826    1% /
/dev/md2             237961216   42010 237919201    1% /data
/dev/md0               64256      45   64211    1% /boot
tmpfs                 514414       1  514413    1% /dev/shm


mdadm --detail /dev/md2

/dev/md2:
        Version : 0.90
  Creation Time : Mon Jun  8 18:14:31 2009
     Raid Level : raid1
     Array Size : 951827072 (907.73 GiB 974.67 GB)
  Used Dev Size : 951827072 (907.73 GiB 974.67 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Wed Aug 18 10:01:27 2010
          State : active
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           UUID : a0bf9972:b46617a2:bf37d07b:5d34b930
         Events : 0.51

    Number   Major   Minor   RaidDevice State
       0       8        2        0      active sync   /dev/sda2
       1       8       18        1      active sync   /dev/sdb2