Power went out during defrag, no space left

mdgm wrote:
Factory reset (wipes all data, settings, everything) and restore data from backup. Or try to expand your volume somehow, run a defrag again, this time preferably with the NAS on a UPS to reduce the risk of an unsafe shutdown in the middle of a defrag and see if the result is any better than after the previous one.

I'll try run the defrag again. It was the first power outage in years, so I doubt it'll happen again.
I've tried googling the problem and some suggest that it could be due to the mounts being mounted on top of already existing data.
Like the md127 mount is placed at /data, but before the mount some data could potentially be stored directly at /data and thereby hidden from the 'du' command but not the 'df' command.. Is this something you've heard about before? They mentioned something about binding the mount to somewhere else and checking, but I wasn't sure exactly how to do that :/

StephenB wrote:

ahkjeldsen wrote: I kinda thought the whole "RAID" thing would take care of when drives died, like giving me a chance to replace the single drive that died. I'm have two WD Red 4 TBs in my NAS and they should be pretty durable - hence I'd be pretty unlucky if they both died at the same time, right? There are other failure modes (for instance NAS chassis, lightening/power surge) which could corrupt/destroy data - not to mention theft/fire/flood. Also, there are many posters here who had a second drive die while waiting for the first replacement to arrive. So it isn't as unusual as you might think. After all, the drives are identical, are in the same chassis, and (thx to the mirroring) have exactly the same usage pattern. So RAID is useful, but not a substitute for backup.

Do you know which drives they've used? Like I'm no hardware expert, so I just bought the drives I could find with the best reviews, the Red drives are optimized or something like that for NAS, so I thought that I would be safe - guess it's just a false sense of security then :/
Most of the files on the NAS is just media files that can be retrieved again from other sources if need be, therefore I didn't really see the need of a backup - though I'd still prefer not having to wipe the whole NAS as it would take plenty of time getting all the media files again.