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Subject: Re: kernel BUG at fs/btrfs/relocation.c:3494
To:     linux-btrfs@vger.kernel.org
References: <b7a45b0ec2f6d034822321734de635f5@hartmark.se>
 <20210123225743.GR31381@hungrycats.org>
From:   Markus Hartung <mail@hartmark.se>
Message-ID: <67a0dcb2-9336-0745-4acc-06d792a0895c@hartmark.se>
Date:   Sun, 24 Jan 2021 23:27:56 +0100
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On 23/01/2021 23:57, Zygo Blaxell wrote:
> You don't have enough space to convert metadata yet, and you also don't
> have enough space to lock one of your 3 metadata block groups without
> running out of global reserve space, so this balance command forces the
> filesystem read-only due to lack of space.
>
>> <snip>
> First you need to get some unallocated space on devid 1, e.g.
>
> 	btrfs balance start -dlimit=12 /
>
> I picked 12 chunks here because your new disk is about 4x the size of
> your old one, so you can expect metadata to expand from 3 GB to 15 GB.
> By moving 12 data chunks to the new disk (plus 3 more from converting
> from dup to raid1), we ensure that space is available for the metadata
> later on.
>
> Once you have some unallocated space on two devices, you can do the
> metadata conversion balance:
>
> 	btrfs balance start -mconvert=raid1,soft /
>
> Every dup chunk converted to raid1 will release more space on devid 1,
> so the balance will complete (as long as you aren't writing hundreds
> of GB of new data at the same time).

Hello,

Thanks for the quick response, I needed obviously reboot a live-os first 
as the / was already mounted, but besides that the balance of some data 
blocks did the trick.

Keep up the good work.

Best regards,

Markus