kernel version:

aleksey@host:~$ sudo uname --all
Linux host 4.15.0-132-generic #136~16.04.1-Ubuntu SMP Tue Jan 12 
18:22:20 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

drive make/model:

Drive is external 5 bay HDD enclosure with raid-5 connected via usb-3 
(made by Orico https://www.orico.cc/us/product/detail/3622.html)
with 5 WD Red 10 Tb. We use this drive for backups.

When i try to run btrfs check i get error message:

aleksey@host:~$ sudo btrfs check --readonly /dev/sdg
Couldn't open file system

aleksey@host:~$ sudo smartctl -x /dev/sdg
smartctl 6.5 2016-01-24 r4214 [x86_64-linux-4.15.0-132-generic] (local 
build)
Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Device Model:     JMicron H/W RAID5
Serial Number:    1IZ6AZCKMIFZYJ8A7V0W
Firmware Version: 0964
User Capacity:    40,003,191,177,216 bytes [40.0 TB]
Sector Size:      512 bytes logical/physical
Device is:        Not in smartctl database [for details use: -P showall]
ATA Version is:   ATA/ATAPI-7 (minor revision not indicated)
Local Time is:    Wed Jan 27 08:51:02 2021 UTC
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
AAM feature is:   Unavailable
APM feature is:   Disabled
Rd look-ahead is: Disabled
Write cache is:   Enabled
ATA Security is:  Disabled, NOT FROZEN [SEC1]
Wt Cache Reorder: Unavailable

=== START OF READ SMART DATA SECTION ===
SMART Status not supported: Incomplete response, ATA output registers 
missing
SMART overall-health self-assessment test result: PASSED
Warning: This result is based on an Attribute check.

General SMART Values:
Offline data collection status:  (0x00) Offline data collection activity
                                         was never started.
                                         Auto Offline Data Collection: 
Disabled.
Total time to complete Offline
data collection:                (    0) seconds.
Offline data collection
capabilities:                    (0x00)         Offline data collection 
not supported.
SMART capabilities:            (0x0000) Automatic saving of SMART 
data                                  is not implemented.
Error logging capability:        (0x00) Error logging NOT supported.
                                         No General Purpose Logging support.

General Purpose Log Directory not supported

SMART Log Directory Version 0
Address    Access  R/W   Size  Description
0x00           SL  R/O      1  Log Directory

SMART Extended Comprehensive Error Log (GP Log 0x03) not supported

SMART Error Log not supported

SMART Extended Self-test Log (GP Log 0x07) not supported

SMART Self-test Log not supported

Selective Self-tests/Logging not supported

SCT Commands not supported

Device Statistics (GP/SMART Log 0x04) not supported

SATA Phy Event Counters (GP Log 0x11) not supported

С уважением,
Алексей Исаев,
RQC

27.01.2021 10:38, Chris Murphy пишет:

On Wed, Jan 27, 2021 at 12:22 AM Alexey Isaev [off-list ref] wrote:

quoted

Hello!

BTRFS volume becomes read-only with this messages in dmesg.
What can i do to repair btrfs partition?

[Jan25 08:18] BTRFS error (device sdg): parent transid verify failed on
52180048330752 wanted 132477 found 132432
[  +0.007587] BTRFS error (device sdg): parent transid verify failed on
52180048330752 wanted 132477 found 132432
[  +0.000132] BTRFS error (device sdg): qgroup scan failed with -5

[Jan25 19:52] BTRFS error (device sdg): parent transid verify failed on
52180048330752 wanted 132477 found 132432
[  +0.009783] BTRFS error (device sdg): parent transid verify failed on
52180048330752 wanted 132477 found 132432
[  +0.000132] BTRFS: error (device sdg) in __btrfs_cow_block:1176:
errno=-5 IO failure
[  +0.000060] BTRFS info (device sdg): forced readonly
[  +0.000004] BTRFS info (device sdg): failed to delete reference to
ftrace.h, inode 2986197 parent 2989315
[  +0.000002] BTRFS: error (device sdg) in __btrfs_unlink_inode:4220:
errno=-5 IO failure
[  +0.006071] BTRFS error (device sdg): pending csums is 430080

What kernel version? What drive make/model?

wanted 132477 found 132432 indicates the drive has lost ~45
transactions, that's not good and also weird. There's no crash or any
other errors? A complete dmesg might be more revealing. And also

smartctl -x /dev/sdg
btrfs check --readonly /dev/sdg

After that I suggest
https://btrfs.wiki.kernel.org/index.php/Restore

And try to get any important data out if it's not backed up. You can
try btrfs-find-root to get a listing of roots, most recent to oldest.
Start at the top, and plug that address in as 'btrfs restore -t' and
see if it'll pull anything out. You likely need -i and -v options as
well.