BTRFS error (device md127): Remounting read-write after error is not allowed
Ok. That command worked on one of my ReadyNAS, although /data was already mounted read/write.
Part of the puzzle here is figuring out why/data was mounted read-only when you booted - e.g. what that error was. Have you tried looking in the log zip? There might be some clues in there.
Another path is to open a support ticket, and have Netgear take it from here.
I had a volume that went read-only because of an error. It took a couple minutes from boot before it went from read-write, so have you tried to jump in really fast and try the deletion? The log should say when it went read-only, so you can see if there is a window of opportunity there.
If you are using Putty, you can re-start the session and the command will still be in the buffer to cursor up and quickly re-execute.
Of course, if it's something else causing it to go read-only other than being full, you'll probably still end up needing to destroy the volume and restore from backup (I did). And doing that would also solve your snapshot problem (though take a long time).
I have created a new volume and I am hoping the issue doesn't reoocur.
A couple of followups...
I do suggest running the maintenance tasks (disk test, balance, scrub, defrag) that you'll find on the volume settings wheel. I run each one once every 3 months on my own NAS. Also, I suggest periodically looking at the SMART stats in the log zip file. OS 6 uses higher thresholds for reallocated/pending sectors than I am comfortable with, and unfortunately those thresholds can't be changed.
If you do use snapshots (which I do), I recommend using the Custom setting (not the SMART setting). Then set a retention period. Unfortunately the SMART snapshots keep the monthly snapshots forever - which will eventually fill the NAS. I find that setting retention to 3 months provides a good balance between recovery of old files and the snapshot storage usage. Though that will depend on your usage. You can adjust the retention for each share.
Most importantly: RAID isn't enough to keep your data safe. The only way to do that is to have at least one backup on another device. So consider putting a backup plan in place.
