Re: Possible Raid Bug

[Anand Jain <anand.jain@oracle.com>]

Hi Patrik,

Thanks for posting a test case. more below.

On 03/26/2016 07:51 PM, Patrik Lundquist wrote:
> So with the lessons learned:
>
> # mkfs.btrfs -m raid10 -d raid10 /dev/sdb /dev/sdc /dev/sdd /dev/sde
>
> # mount /dev/sdb /mnt; dmesg | tail
> # touch /mnt/test1; sync; btrfs device usage /mnt
>
> Only raid10 profiles.
>
> # echo 1 >/sys/block/sde/device/delete
>
> We lost a disk.
>
> # touch /mnt/test2; sync; dmesg | tail
>
> We've got write errors.
>
> # btrfs device usage /mnt
>
> No 'single' profiles because we haven't remounted yet.
>
> # reboot
> # wipefs -a /dev/sde; reboot
>
> # mount -o degraded /dev/sdb /mnt; dmesg | tail
> # btrfs device usage /mnt
>
> Still only raid10 profiles.
>
> # touch /mnt/test3; sync; btrfs device usage /mnt
>
> Now we've got 'single' profiles. Replace now or get hosed.

  Since you are replacing the failed device without mount/unmount/reboot,
  so this should work.

  And you would need those parts of hot spare/auto replace patches only
  if the test case had unmount/mount or reboot at this stage.


> # btrfs replace start -B 4 /dev/sde /mnt; dmesg | tail
>
> # btrfs device stats /mnt
>
> [/dev/sde].write_io_errs   0
> [/dev/sde].read_io_errs    0
> [/dev/sde].flush_io_errs   0
> [/dev/sde].corruption_errs 0
> [/dev/sde].generation_errs 0
>
> We didn't inherit the /dev/sde error count. Is that a bug?

   No. Its other way, it would have been a bug if the replace-target
   inherited the error counters.

> # btrfs balance start -dconvert=raid10,soft -mconvert=raid10,soft
> -sconvert=raid10,soft -vf /mnt; dmesg | tail
>
> # btrfs device usage /mnt
>
> Back to only 'raid10' profiles.
>
> # umount /mnt; mount /dev/sdb /mnt; dmesg | tail
>
> # btrfs device stats /mnt
>
> [/dev/sde].write_io_errs   11
> [/dev/sde].read_io_errs    0
> [/dev/sde].flush_io_errs   2
> [/dev/sde].corruption_errs 0
> [/dev/sde].generation_errs 0
>
> The old counters are back. That's good, but wtf?

  No. I doubt if they are old counters. The steps above didn't
  show old error counts, but since you have created a file
  test3 so there will be some write_io_errors, which we don;t
  see after the balance. So I doubt if they are old counter
  but instead they are new flush errors.

> # btrfs device stats -z /dev/sde
>
> Give /dev/sde a clean bill of health. Won't warn when mounting again.




Thanks, Anand