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.

quoted

<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