Re: What mechanisms protect against split brain?

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

I tried some test about this case.

After the missing RAID1 device is re-introduced,
1, mount/read seem to work.
   checksum based error detect help.
   current pid based i/o patch select policy may help too.
       preferred_mirror = first + (current->pid % num_stripes);

2, 'btrfs scrub' failed to finish.
    Any advice to return to clean state?

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2022/06/08

> Hi,
> 
> Recently there have been some discussions, both here on the mailing list and on #btrfs IRC, about the consequences of mounting one RAID1 mirror as degraded and then later re-introduce the missing device. But also on having degraded mount option in fstab and kernel command line.
> 
> So I wonder if Btrfs has some protective mechanisms against data loss/corruption if a drive is missing for a bit but later re-introduced. There is also the case of split brain where each mirror might be independently updated and then recombined.
> 
> Is there an official recommendation to have with regards to degraded mounts from kernel command line? I understand the use case as it allows the system to boot even if a device goes missing or dead after a reboot.
> 
> Thanks,
> Forza