As mentioned the 4TB Barracuda is an SMR drive. These are pretty useless for RAID as their write speeds are abysmal. In case a resilver is needed it'd take like 10 times longer than with CMR drives, completely defeating the point of RAID. See https://www.servethehome.com/wd-red-smr-vs-cmr-tested-avoid-red-smr/

At least ZFS allows increasing the size of the drives within a mirror pool. Not sure about other RAID setups but it's a pretty easy feature to support so I would expect virtually everything to have it.

You need at least like 5-6 drives for double parity to be economical. Aside from that you need backup.

You might be able to save the data, with minor chunks missing. The drive, not so much.

Use a Windows machine and chkdsk.

NEVER do that

For good measure you can do a surface scan too

yea, sure, kill it completely

Yes, it's one of the worst portable drives line to ever exist.

Also, see https://www.backblaze.com/blog/drive-failure-over-time-the-bathtub-curve-is-leaking/

I'd be surprised if you'd be legally allowed to handle such data with any of the programs suggested here. It'd be best if you reached out to whoever is responsible in your department.

this generally happens when you buy the trashiest externals on the market

any transcoding in this setup would be an indication of a configuration or plex error

80 ms grey to grey response time? What the fuck?! How are people praising this display everywhere? That puts it close to unusable. It's 5 frames at 60Hz...

One ZFS drive per pool, with unraid on top? Should be mostly fine. As you say these drives are terrible for writes, but they should be pretty reliable and performant for your workload.

I'd expect that to be permanent.

they are not selling your data, that would be dumb