There is an easy way out (i did this already):
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Dont do anything rw with the broken btrfs volume
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Boot a recovery system (DVD or USB …)
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mount your defect btrfs volume as ro (this can be handled already as a snapshot)
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List all subvolumes accesible on your volume (take @ or whatever is the subvolume with your data on it. You can browse it ro !!!)
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mount a empty backup-btrfs volume rw
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transfer the complete btrfs-volume with btrfs send to the new volume.
This way you won´t loose any data
Best of all, the backup volume can be smaller or larger than the original volume. Only the data actually used has to fit on it -
check your backup !
6.If you think you can fix it. You can try now. But if it fails, you can move on to the next step -
reformat the original btrfs volume again with btrfs
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mount the backup ro
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transfer the backup back with btrfs send
btrfs send only transmits the data that is used and is therefore faster than most other backup programs
Tips for the future:
- If you are afraid that your data may have been corrupted: use btrfs scrub
- Please use btrfs balance very sparingly. This is mostly unnecessary and only loads the system. If, btrfs balance, then use it with limits e.g. 50%
- Take automatic snapshots (e.g. with snapper) every hour if possible. At btrfs it doesn’t cost anything. Snapper can also automatically remove these snapshots after some time.
You can find good information at btrfs at kernel-org and in the arch-wiki
Viel Erfolg 