OK, Sunil, you proved your disk array is 10 Terabytes. So if it is
12 1 terabyte disks you set it up RAID 6. You carved out a partition
of 8 terabytes (1024) based or 8,8 terabytes 1024 based leaving only
1.2 terabytes, which I believe is very close to what you said you saw.
The rest may be the automatic 10% margin for root purposes Linux that
keeps on disks.

{^_^}

On 2011/06/06 04:25, Sunil M. Dogra wrote:
> Disk /dev/cciss/c0d1: 10001.7 GB, 10001711325184 bytes
> 255 heads, 63 sectors/track, 1215972 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
>
>             Device Boot      Start         End      Blocks   Id  System
> /dev/cciss/c0d1p1               1      267350  2147483647+  ee  EFI GPT