Not able to run fsck on root file system

I am trying to root disk mirroring on SunFire V210 Server. There are two disks on this server c1t0d0 and c1t1d0 . I completed all the steps and I updated the vfstab file too. After I have updated the vfstab file I run df -h command but could not see the changes i made in vfstab. Suddenly the server got rebooted automatically and I could not boot the server. So I put the solaris 10 cd and did boot cdrom -s and mount /dev/dsk/c1t0d0s0 /a . Then I tried to do the fsck /dev/dsk/c1t0d0s0 but could not do that. c1t0d0s0 has the mount point /. Could any one give me a hint or suggestion on why I cant run fsck command.thanks in advance.
:wall:

# fsck /dev/dsk/c1t0d0s0
NOTICE: /a: unexpected free inode 1476, run fsck(1M)
NOTICE: /a: unexpected free inode 1476, run fsck(1M)
NOTICE: /a: unexpected free inode 1476, run fsck(1M)
/dev/dsk/c1t0d0s0 IS CURRENTLY MOUNTED READ/WRITE.
CONTINUE? y

** /dev/dsk/c1t0d0s0
BAD SUPERBLOCK AT BLOCK 16: NUMBER OF DIRECTORIES OUT OF RANGE

LOOK FOR ALTERNATE SUPERBLOCKS WITH MKFS? y

calcsb: short read of superblock from mkfs

LOOK FOR ALTERNATE SUPERBLOCKS WITH NEWFS? y

SEARCH FOR ALTERNATE SUPERBLOCKS FAILED.

USE GENERIC SUPERBLOCK FROM MKFS? y

calcsb: short read of superblock from mkfs

USE GENERIC SUPERBLOCK FROM NEWFS?

SEARCH FOR ALTERNATE SUPERBLOCKS FAILED. YOU MUST USE THE -o b OPTION
TO FSCK TO SPECIFY THE LOCATION OF A VALID ALTERNATE SUPERBLOCK TO
SUPPLY NEEDED INFORMATION; SEE fsck(1M).

i can see the mistakes you are doing here.

fsck should never be run on mounted FS.
There is no need to mount the root FS before fscking.
Unmount and run again.

Also it should be fsck /dev/rdsk/....

Please paste the output also.