Re: Adventures in btrfs raid5 disk recovery

[Roman Mamedov <rm@romanrm.net>]

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On Sun, 19 Jun 2016 23:44:27 -0400
Zygo Blaxell <ce3g8jdj@umail.furryterror.org> wrote:

> It's not going well so far.  Pay attention, there are at least four
> separate problems in here and we're not even half done yet.
> 
> I'm currently using kernel 4.6.2 with btrfs fixes forward-ported from
> 4.5.7, because 4.5.7 has a number of fixes that 4.6.2 doesn't.  I have
> also pulled in some patches from the 4.7-rc series.
> 
> This fixed a few problems I encountered early on, and I'm still making
> forward progress, but I've only replaced 50% of the failed disk so far,
> and this is week four of this particular project.

From a practical standpoint, [aside from not using Btrfs RAID5], you'd be
better off shutting down the system, booting a rescue OS, copying the content
of the failing disk to the replacement one using 'ddrescue', then removing the
bad disk, and after boot up your main system wouldn't notice anything has ever
happened, aside from a few recoverable CRC errors in the "holes" on the areas
which ddrescue failed to copy.

But in general it's commendable that you're experimenting with doing things
"the native way", as this is provides feedback to the developers and could help
make the RAID implementation better. I guess that's the whole point of the
exercise and the report, and hope this ends up being useful for everyone.

-- 
With respect,
Roman

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