BTRFS repair - mount wrong fs type

@markus wrote:

Hi,

my RAID 5 with 4 disks has one disk failure. I thought, okay, no problem, change it and it will be ok. I’ve done it once, so it should be no problem, but i’ve proven me wrong.

The bad disk is sdb(devid 4)
And when i try to mount the FS in degraded mode, it says wrong fs type.
device /dev/sda: failed to read chunk tree -5
device /dev/sda: open_ctree failed

Outputs:

[root@nas ~]# btrfs fi show
Label: 'rockstor_rockstor'  uuid: d323aac9-d70a-4022-a631-49f3082380bb
    Total devices 1 FS bytes used 3.80GiB
    devid    1 size 49.82GiB used 34.30GiB path /dev/sde3

warning, device 4 is missing
bytenr mismatch, want=12944226566144, have=12944226762752
Couldn't read chunk tree
Label: 'store'  uuid: 7a358cf9-41f2-466c-9629-57b15daf8337
    Total devices 4 FS bytes used 7.36TiB
    devid    3 size 3.64TiB used 2.69TiB path /dev/sda
    devid    5 size 3.64TiB used 2.69TiB path /dev/sdc
    devid    6 size 3.64TiB used 2.69TiB path /dev/sdd
    *** Some devices missing

[root@nas ~]# mount -o degraded /dev/sda /mnt2/store
mount: wrong fs type, bad option, bad superblock on /dev/sda,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

dmesg:
[ 1230.494748] BTRFS info (device sda): allowing degraded mounts
[ 1230.494752] BTRFS info (device sda): disk space caching is enabled
[ 1230.494753] BTRFS info (device sda): has skinny extents
[ 1230.638994] BTRFS info (device sda): bdev (null) errs: wr 1767, rd 695, flush 514, corrupt 0, gen 0
[ 1230.638998] BTRFS info (device sda): bdev /dev/sda errs: wr 0, rd 251, flush 0, corrupt 0, gen 0
[ 1231.359262] BTRFS error (device sda): bad tree block start 0 21167414001664
[ 1231.360643] BTRFS error (device sda): failed to read block groups: -5
[ 1231.395040] BTRFS error (device sda): open_ctree failed

Nothing helped so far. I’ve tried chunk recover, zero-log.
And I already searched all similar threads, but nowhere I found a solution.

Is there any chance, to recover the raid?

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