Re: Tried to replace a drive in a raid 1 and all hell broke loose

[Nicholas D Steeves <nsteeves@gmail.com>]

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Hi Chris, Efkf, Duncan, and anyone else reading this,

Chris Murphy <lists@colorremedies.com> writes:

>>#btrfs fi df /mnt/sd/
>>Data, RAID1: total=772.00GiB, used=771.22GiB
>>Data, single: total=1.00GiB, used=2.25MiB
>>System, RAID1: total=32.00MiB, used=96.00KiB
>>System, single: total=32.00MiB, used=48.00KiB
>>Metadata, RAID1: total=3.00GiB, used=1.54GiB
>>Metadata, single: total=1.00GiB, used=0.00B
>
> This is not good. Some of the data and some of the metadata
> (specifically system profile which is the chunk tree) is only
> available on one drive and I can't tell from this if it's on a drive
> that is missing or is spewing errors. Anything that has a single copy
> that's also damaged, cannot be recovered. Unfortunately this file
> system is not completely raid1 and that's likely one source of the
> problem. The chunk tree is really critical so if any part of it is bad
> and not redundant (no good copy) the file system is not likely
> repairable. Get the data out as best you can. If rescue=all mount
> option doesn't work, the next opportunity is btrfs restore, but it too
> depends on the chunk tree being intact. There is a 'btrfs restore
> chunk-tree' option that will scan all the drives looking for plausible
> fragments of the chunk tree to try and recover it but it takes a long
> time (hours).
>
> 48KiB of chunk tree, if it's corrupt, is quite a lot and might prevent
> quite a lot of recovery. Some older kernels would create single
> profile chunks when a raid1 file system was mounted in degraded,rw
> mode with a missing device. This happens silently. And then when the
> raid1 is back to full strength again, there's no automatic conversion
> or even a warning by the kernel that this critical metadata isn't
> redundant still. The burden right now is unfortunately on the user to
> identify this reduction in redundancy and make sure to do a filtered
> balance to convert the single chunks into raid1 chunks.
>

I reported this issue "Wed, 02 Mar 2016 20:25:46 -0500" with Subject
"incomplete conversion to RAID1?", and it now looks that there's
evidence that this bug isn't harmless after all.

Efkf, would you please confirm if the filesystem was created with Linux
and btrfs-progs 5.10.x? (please keep me in CC)

If anyone knows if this issue was fixed for 5.15, please share the good
news!


Regards,
Nicholas

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