Why File system is showing Less space than the actual disk

Query:  Why /storage FS is showing Only 4 TB of Storage, where From storage 5 TB space is allocated.

/dev/md0              4.0T  2.7T  1.4T  67% /storage

1.   Following disks are assigned to the Server with 2.5 TB Each.

Disk /dev/sda: 2498.0 GB, 2498090418176 bytes

Disk /dev/sdb: 2497.6 GB, 2497603174400 bytes

2.   However the Disks are formatted with fdisk, which supports maximum size of 2.2 TB.

Disk /dev/sda1: 2199.0 GB, 2199020350464 bytes

Disk /dev/sdb1: 2199.0 GB, 2199020350464 bytes

3.   We have RAID(md0) on this 2 disks, so Logically we should have 4.4 TB Space for File system.

/dev/md0:

        Version : 0.90

  Creation Time : Wed Jan 14 12:05:53 2009

     Raid Level : raid0

     Array Size : 4294961152 (4095.99 GiB 4398.04 GB)

   Raid Devices : 2

  Total Devices : 2

    Update Time : Wed Jan 14 12:05:53 2009

          State : clean

Active Devices : 2

Working Devices : 2

Chunk Size : 256K

UUID : a70ea626:0a5c99d8:8fe9e169:8540d711

 Events : 0.1

Number   Major   Minor   RaidDevice State

  0       8        1        0      active sync   /dev/sda1

  1       8       17        1      active sync   /dev/sdb1

4.   However Metadata version 0.90 has following Limitations, so we cannot use  beyond 4 TB Storage space.

Version 0.90 Metadata Limitations:

    28 devices maximum in one array

    each device may be a maximum of 2 TiB in size

    No support for bad-block-management

Solution/Recommendations For using Full capacity:

1.   We need to back up the data.

2.   Delete the RAID.

3.   Format the disk with parted.

4.   Update the OS to Kernel Version 2.6.27 or Higher     

And/OR

5.   Create the RAID with updated metadata version 1 or 3 (It is latest)

6.   Then create the File system.

7.   Restore the Data.