i want to mount a raid1 with 2x 4TB btrfs-HDD and it fails with "invalid argument".
The System is an AlpineLinux running on a SBC for a small Nextcloud.
btrfsck said /dev/sdb had Checksum verify fail, bad tree block and a Chunk-Root-Error, so i chose to remove the disk, zap the superblocks, reformat it and add it again. Now its clean again:

Opening filesystem to check...
Checking filesystem on /dev/sdb1
UUID: d6899d0f-0771-45dc-a917-dc5bc635273a
[1/8] checking log skipped (none written)
[2/8] checking root items
[3/8] checking extents
[4/8] checking free space tree
[5/8] checking fs roots
[6/8] checking only csums items (without verifying data)
[7/8] checking root refs
[8/8] checking quota groups skipped (not enabled on this FS)
found 147456 bytes used, no error found
total csum bytes: 0
total tree bytes: 147456
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 140646
file data blocks allocated: 0
 referenced 0

This is /proc/mdstat

/home/sysad # cat /proc/mdstat 
Personalities : [raid1] 
md127 : active (auto-read-only) raid1 sdb1[2](S) sda1[0]
      3906884608 blocks super 1.2 [2/1] [U_]
      bitmap: 0/30 pages [0KB], 65536KB chunk

unused devices: 

Here is the dmesg output in a bin.

This is from mdadm --examine:

/home/sysad # mdadm --examine /dev/sdb1 
/dev/sdb1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x3
     Array UUID : a92785da:ba629f92:b1965688:3d8c636e
           Name : dirc:dataraid  (local to host dirc)
  Creation Time : Sat Dec 13 00:48:15 2025
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 7813769216 sectors (3.64 TiB 4.00 TB)
     Array Size : 3906884608 KiB (3.64 TiB 4.00 TB)
    Data Offset : 264192 sectors
   Super Offset : 8 sectors
Recovery Offset : 48606208 sectors
   Unused Space : before=264112 sectors, after=0 sectors
          State : clean
    Device UUID : 52deea94:02d8e7b0:53cf6bd7:330f9f23

Internal Bitmap : 8 sectors from superblock
    Update Time : Tue Dec 16 20:04:43 2025
  Bad Block Log : 512 entries available at offset 24 sectors
       Checksum : 8048178 - correct
         Events : 21541


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

This is mdadm --detail:

/dev/md/dataraid:
           Version : 1.2
     Creation Time : Sat Dec 13 00:48:15 2025
        Raid Level : raid1
        Array Size : 3906884608 (3.64 TiB 4.00 TB)
     Used Dev Size : 3906884608 (3.64 TiB 4.00 TB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Tue Dec 16 20:04:43 2025
             State : clean, degraded 
    Active Devices : 1
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 1

Consistency Policy : bitmap

              Name : dirc:dataraid  (local to host dirc)
              UUID : a92785da:ba629f92:b1965688:3d8c636e
            Events : 21541

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       -       0        0        1      removed

       2       8       17        -      spare   /dev/sdb1

Did i forget something? Advice on how to proceed would be very much appreciated.

dijak