Mdadm raid 5 array tem metade do tamanho do esperado

Criei um array Raid 5 com mdadm consistindo em 4 unidades de 4 TB, esperava que o array tivesse 11-12 TB no espaço total.

Mas depois de construir o array, notei que ele tem metade do tamanho esperado com apenas 6 TB. E cada unidade está sendo exibida como 2 TB utilizáveis.

Configuração de invasão:

$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10] 
md127 : active raid5 sdc1[1] sda1[4] sdd1[2] sdb1[0]
      6442051584 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
      bitmap: 1/16 pages [4KB], 65536KB chunk

unused devices: <none>

$ mdadm --detail /dev/md127
/dev/md127:
           Version : 1.2
     Creation Time : Tue Jul 25 10:24:33 2023
        Raid Level : raid5
        Array Size : 6442051584 (6143.62 GiB 6596.66 GB)
     Used Dev Size : 2147350528 (2047.87 GiB 2198.89 GB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Sat Aug  5 00:10:25 2023
             State : clean 
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 512K

Consistency Policy : bitmap

              Name : explorer:0  (local to host explorer)
              UUID : bd6ea5b8:e20be480:40c7cf15:514e6dec
            Events : 2734

    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        1        3      active sync   /dev/sda1

todos os discos usados ​​no array

$ fdisk -l

Disk /dev/sdd: 3.64 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: HGST HUS724040AL
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x93cf7f24

Device     Boot Start        End    Sectors Size Id Type
/dev/sdd1        2048 4294967295 4294965248   2T fd Linux raid autodetect


Disk /dev/sdb: 3.64 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: HGST HUS724040AL
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x35a7a3cc

Device     Boot Start        End    Sectors Size Id Type
/dev/sdb1        2048 4294967295 4294965248   2T fd Linux raid autodetect


Disk /dev/sda: 3.64 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: HGST HUS724040AL
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xfa31510a

Device     Boot Start        End    Sectors Size Id Type
/dev/sda1        2048 4294967295 4294965248   2T fd Linux raid autodetect


Disk /dev/sdc: 3.64 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: HGST HUS724040AL
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x584e9ded

Device     Boot Start        End    Sectors Size Id Type
/dev/sdc1        2048 4294967295 4294965248   2T fd Linux raid autodetect


Disk /dev/md127: 6 TiB, 6596660822016 bytes, 12884103168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1572864 bytes

Não faz sentido porque o ataque teria metade do tamanho que eu esperava.

Como posso descobrir por que esse é o caso e/ou obter o tamanho total esperado.