raid5 size reduced after system reinstall, how to fix?

[Marcus Lell <marcus.lell@xxxxxxxxx>]

Hello,

after reinstalling gentoo on my main system,
I had to find out, that my clean raid5 has been resized
from ca. 18,2TB to ca. 2,2 TB
.
I don't have any clue, why..

First, the array gets assembled successfully.

lxcore ~ # cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[2] sdb1[1] sdc1[0]
      2352740224 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
      bitmap: 0/9 pages [0KB], 65536KB chunk

unused devices: <none>

lxcore ~ # mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Sat Nov 10 23:04:14 2018
        Raid Level : raid5
        Array Size : 2352740224 (2243.75 GiB 2409.21 GB)
     Used Dev Size : 1176370112 (1121.87 GiB 1204.60 GB)
      Raid Devices : 3
     Total Devices : 3
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Tue Jan 12 14:58:40 2021
             State : clean
    Active Devices : 3
   Working Devices : 3
    Failed Devices : 0
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 64K

Consistency Policy : bitmap

              Name : lxcore:0  (local to host lxcore)
              UUID : 0e3c432b:c68cda5b:0bf31e79:9dfe252b
            Events : 80471

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

but the partitions are ok

lxcore ~ # fdisk -l /dev/sdb1
Disk /dev/sdb1: 9.1 TiB, 10000830283264 bytes, 19532871647 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

same with sdc1 and sdd1
Here is the problem:

lxcore ~ # mdadm --examine /dev/sdb1
/dev/sdb1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x1
     Array UUID : 0e3c432b:c68cda5b:0bf31e79:9dfe252b
           Name : lxcore:0  (local to host lxcore)
  Creation Time : Sat Nov 10 23:04:14 2018
     Raid Level : raid5
   Raid Devices : 3

 Avail Dev Size : 19532609759 (9313.87 GiB 10000.70 GB)
     Array Size : 2352740224 (2243.75 GiB 2409.21 GB)
  Used Dev Size : 2352740224 (1121.87 GiB 1204.60 GB)
    Data Offset : 261888 sectors
   Super Offset : 8 sectors
   Unused Space : before=261800 sectors, after=17179869535 sectors
          State : clean
    Device UUID : a8fbe4dd:a7ac9c16:d1d29abd:e2a0d573

Internal Bitmap : 8 sectors from superblock
    Update Time : Tue Jan 12 14:58:40 2021
  Bad Block Log : 512 entries available at offset 72 sectors
       Checksum : 86f42300 - correct
         Events : 80471

         Layout : left-symmetric
     Chunk Size : 64K

   Device Role : Active device 1
   Array State : AAA ('A' == active, '.' == missing, 'R' == replacing)

same with /dev/sdc1 and /dev/sdd1
It shows, that only 1121.68GB are used instead of the
available 9.1TB, so the array size results in 2.2TB


Will a simple
mdadm --grow --size=max /dev/md0
fix this and leave the data untouched?

Any further advice?

Have a nice day.

marcus

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