Raid 5アレイのスペースがディスクの合計と等しくないのはなぜですか？

4つのディスクからRAID 5を作成しようとしています。

Disk /dev/sdc: 8001.6 GB, 8001563222016 bytes
/dev/sdc1            2048  4294967294  2147482623+  fd  Linux raid autodetect
Disk /dev/sdb: 8001.6 GB, 8001563222016 bytes
/dev/sdb1            2048  4294967294  2147482623+  fd  Linux raid autodetect
Disk /dev/sdd: 24003.1 GB, 24003062267904 bytes
/dev/sdd1            2048  4294967294  2147482623+  fd  Linux raid autodetect
Disk /dev/sde: 8001.6 GB, 8001563222016 bytes
/dev/sde1            2048  4294967294  2147482623+  fd  Linux raid autodetect

しかし、作成後は6Tのスペースのみを確保しました（私のディスクの1つ）。

/dev/md0         ext4   6.0T  184M  5.7T   1% /mnt/raid5

私の作成プロセスに関する追加情報は次のとおりです。

結果mdadm -E /dev/sd[b-e]1:

/dev/sdb1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d
           Name : node7:0  (local to host node7)
  Creation Time : Fri Sep  7 09:16:42 2018
     Raid Level : raid5
   Raid Devices : 4

 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB)
     Array Size : 6442053120 (6143.62 GiB 6596.66 GB)
  Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
          State : clean
    Device UUID : 2fcb3346:9ed69eab:64c6f851:0bcc39c4

    Update Time : Fri Sep  7 13:17:38 2018
       Checksum : c701ff7e - correct
         Events : 18

         Layout : left-symmetric
     Chunk Size : 512K

   Device Role : Active device 0
   Array State : AAAA ('A' == active, '.' == missing)
/dev/sdc1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d
           Name : node7:0  (local to host node7)
  Creation Time : Fri Sep  7 09:16:42 2018
     Raid Level : raid5
   Raid Devices : 4

 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB)
     Array Size : 6442053120 (6143.62 GiB 6596.66 GB)
  Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
          State : clean
    Device UUID : 6f13c9f0:de2d4c6f:cbac6b87:67bc483e

    Update Time : Fri Sep  7 13:17:38 2018
       Checksum : e4c675c2 - correct
         Events : 18

         Layout : left-symmetric
     Chunk Size : 512K

   Device Role : Active device 1
   Array State : AAAA ('A' == active, '.' == missing)
/dev/sdd1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d
           Name : node7:0  (local to host node7)
  Creation Time : Fri Sep  7 09:16:42 2018
     Raid Level : raid5
   Raid Devices : 4

 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB)
     Array Size : 6442053120 (6143.62 GiB 6596.66 GB)
  Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
          State : clean
    Device UUID : 4dab38e6:94c5052b:06d6b6b0:34a41472

    Update Time : Fri Sep  7 13:17:38 2018
       Checksum : f306b65f - correct
         Events : 18

         Layout : left-symmetric
     Chunk Size : 512K

   Device Role : Active device 2
   Array State : AAAA ('A' == active, '.' == missing)
/dev/sde1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d
           Name : node7:0  (local to host node7)
  Creation Time : Fri Sep  7 09:16:42 2018
     Raid Level : raid5
   Raid Devices : 4

 Avail Dev Size : 4294703103 (2047.87 GiB 2198.89 GB)
     Array Size : 6442053120 (6143.62 GiB 6596.66 GB)
  Used Dev Size : 4294702080 (2047.87 GiB 2198.89 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
          State : clean
    Device UUID : b04d152e:0448fe56:3b22a2d6:b2504d26

    Update Time : Fri Sep  7 13:17:38 2018
       Checksum : 40ffd3e7 - correct
         Events : 18

         Layout : left-symmetric
     Chunk Size : 512K

   Device Role : Active device 3
   Array State : AAAA ('A' == active, '.' == missing)

結果mdadm --detail /dev/md0:

/dev/md0:
        Version : 1.2
  Creation Time : Fri Sep  7 09:16:42 2018
     Raid Level : raid5
     Array Size : 6442053120 (6143.62 GiB 6596.66 GB)
  Used Dev Size : 2147351040 (2047.87 GiB 2198.89 GB)
   Raid Devices : 4
  Total Devices : 4
    Persistence : Superblock is persistent

    Update Time : Fri Sep  7 13:17:38 2018
          State : clean 
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : node7:0  (local to host node7)
           UUID : 8953b4f1:61212c46:b0a63144:25eb4a7d
         Events : 18

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8       33        1      active sync   /dev/sdc1
       2       8       49        2      active sync   /dev/sdd1
       4       8       65        3      active sync   /dev/sde1

結果mkfs.ext4 /dev/md0

mke2fs 1.41.9 (22-Aug-2009)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
402628608 inodes, 1610513280 blocks
80525664 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
49149 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks: 
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
    4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 
    102400000, 214990848, 512000000, 550731776, 644972544

Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: 
done

This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

そしてmkdir /mnt/raid5。mount /dev/md0 /mnt/raid5/