Scrub: Meaning of 1 error detected?

[Forza-tng]

Hi,

I had a device (/dev/sdaj) ejected by HBA due to too low device timeout. After some time I rebooted and ran a scrub to fixup the data that was lost on the missing raid member.

When scrub finished, it reported WARNING: errors detected during scrubbing, 1 corrected. My question is if this mean 1 error or 1 device being corrected? The actual number of corrected blocks were in fact 121582377.

I will not be able to reprocuce the issue on this system as it is a production machine. Since it is clear from btrfs scrub status how many corrections were made, I think this issue is mostly cosmetical.

❯ btrfs scrub status /mnt/nas_hdd/
UUID:             7745e2f7-5c67-4b18-844b-8e93399f7b0b
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         24:25:33
Total to scrub:   91.54TiB
Rate:             1.05GiB/s
Error summary:    csum=121582377
  Corrected:      121582377
  Uncorrectable:  0
  Unverified:     0

The filesystem is using RAID10 profile with the btrfs allocation hints patches on kernel 6.12.7. Btrfs progs v6.10.1.

❯ btrfs fi us -T /mnt/nas_hdd/
Overall:
    Device size:                 169.00TiB
    Device allocated:             93.53TiB
    Device unallocated:           75.47TiB
    Device missing:                  0.00B
    Device slack:                 11.85TiB
    Used:                         91.48TiB
    Free (estimated):             38.75TiB      (min: 26.17TiB)
    Free (statfs, df):            38.72TiB
    Data ratio:                       2.00
    Metadata ratio:                   3.00
    Global reserve:              512.00MiB      (used: 0.00B)
    Multiple profiles:                  no

              Data     Metadata  System
Id Path       RAID10   RAID1C3   RAID1C3  Unallocated Total     Slack
-- ---------- -------- --------- -------- ----------- --------- ---------
11 /dev/sdi1   8.62TiB         -        -     7.74TiB  16.36TiB  10.00GiB
12 /dev/sdc1   8.62TiB         -        -     7.74TiB  16.36TiB  10.00GiB
13 /dev/sdn1   8.62TiB         -        -     7.74TiB  16.36TiB  10.00GiB
14 /dev/sdv1   8.62TiB         -        -     7.74TiB  16.36TiB  10.00GiB
15 /dev/sdad1 11.44TiB         -        -     4.92TiB  16.36TiB   1.83TiB
16 /dev/sdaj1 11.44TiB         -        -     4.92TiB  16.36TiB   1.83TiB
17 /dev/sdah1  8.62TiB         -        -     7.74TiB  16.36TiB   1.83TiB
18 /dev/sdaf1  8.62TiB         -        -     7.74TiB  16.36TiB   1.83TiB
19 /dev/sdac1  8.62TiB         -        -     7.74TiB  16.36TiB   1.83TiB
20 /dev/sdae1  8.62TiB         -        -     7.74TiB  16.36TiB   1.83TiB
21 /dev/sdl1         - 338.00GiB        -   556.25GiB 894.25GiB         -
22 /dev/sdf1         - 336.00GiB        -   558.25GiB 894.25GiB         -
23 /dev/sdu1         - 352.00GiB        -   579.51GiB 931.51GiB         -
24 /dev/sds1         - 307.00GiB 32.00MiB   624.48GiB 931.51GiB         -
25 /dev/sdy1         - 311.00GiB 32.00MiB   620.48GiB 931.51GiB         -
26 /dev/sdag1        -  39.00GiB 32.00MiB   892.48GiB 931.51GiB 856.98GiB
-- ---------- -------- --------- -------- ----------- --------- ---------
   Total      45.94TiB 561.00GiB 32.00MiB    75.47TiB 169.00TiB  11.85TiB
   Used       44.93TiB 552.93GiB  4.42MiB

This is the full output of scrub

❯ btrfs scrub start -d -B -c 0 /mnt/nas_hdd/
Starting scrub on devid 11
Starting scrub on devid 12
Starting scrub on devid 13
Starting scrub on devid 14
Starting scrub on devid 15
Starting scrub on devid 16
Starting scrub on devid 17
Starting scrub on devid 18
Starting scrub on devid 19
Starting scrub on devid 20
Starting scrub on devid 21
Starting scrub on devid 22
Starting scrub on devid 23
Starting scrub on devid 24
Starting scrub on devid 25
Starting scrub on devid 26

Scrub device /dev/sdi1 (id 11) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         11:20:24
Total to scrub:   8.37TiB
Rate:             214.97MiB/s
Error summary:    no errors found

Scrub device /dev/sdc1 (id 12) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         11:55:08
Total to scrub:   8.37TiB
Rate:             204.54MiB/s
Error summary:    no errors found

Scrub device /dev/sdn1 (id 13) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         11:17:50
Total to scrub:   8.37TiB
Rate:             215.79MiB/s
Error summary:    no errors found

Scrub device /dev/sdv1 (id 14) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         11:17:15
Total to scrub:   8.37TiB
Rate:             215.97MiB/s
Error summary:    no errors found

Scrub device /dev/sdad1 (id 15) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         15:23:15
Total to scrub:   10.98TiB
Rate:             207.76MiB/s
Error summary:    no errors found

Scrub device /dev/sdaj1 (id 16) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         24:25:33
Total to scrub:   10.98TiB
Rate:             130.96MiB/s
Error summary:    csum=121582377
  Corrected:      121582377
  Uncorrectable:  0
  Unverified:     0

Scrub device /dev/sdah1 (id 17) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         10:59:33
Total to scrub:   8.37TiB
Rate:             221.79MiB/s
Error summary:    no errors found

Scrub device /dev/sdaf1 (id 18) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         10:57:36
Total to scrub:   8.37TiB
Rate:             222.44MiB/s
Error summary:    no errors found

Scrub device /dev/sdac1 (id 19) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         11:13:10
Total to scrub:   8.37TiB
Rate:             217.31MiB/s
Error summary:    no errors found

Scrub device /dev/sdae1 (id 20) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         11:12:05
Total to scrub:   8.37TiB
Rate:             217.66MiB/s
Error summary:    no errors found

Scrub device /dev/sdl1 (id 21) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         0:14:51
Total to scrub:   332.74GiB
Rate:             382.41MiB/s
Error summary:    no errors found

Scrub device /dev/sdf1 (id 22) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         0:14:54
Total to scrub:   331.07GiB
Rate:             379.21MiB/s
Error summary:    no errors found

Scrub device /dev/sdu1 (id 23) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         0:15:29
Total to scrub:   346.47GiB
Rate:             381.90MiB/s
Error summary:    no errors found

Scrub device /dev/sds1 (id 24) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         0:14:50
Total to scrub:   298.95GiB
Rate:             343.96MiB/s
Error summary:    no errors found

Scrub device /dev/sdy1 (id 25) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         0:14:58
Total to scrub:   302.92GiB
Rate:             345.43MiB/s
Error summary:    no errors found

Scrub device /dev/sdag1 (id 26) done
Scrub started:    Thu Jan  9 18:10:12 2025
Status:           finished
Duration:         0:01:58
Total to scrub:   37.88GiB
Rate:             328.74MiB/s
Error summary:    no errors found
WARNING: errors detected during scrubbing, 1 corrected