JonathanM

Can you recreate in safe mode? There are so many plugins and modifications it's tough to say whether this is Unraid or one of the modifications causing it.

Cancel anytime you want, won't effect anything. Replacement disks don't need to be all zero, that's only needed for adding data slots. See trurl's post above yours.

What is the intended destination of this drive?

Correcting involves reading the data disks and writing data to the parity drive. Until you have completely repeatable parity checks returning identical results on subsequent runs,

Unbalance plugin.

If 2 consecutive non- correcting checks come back with different error addresses, you shouldn't run a correcting check until you figure out why you are getting errors and correct the issue. As was already stated, the most common cause for this type of thing is unreliable RAM, but that can be caused by unstable power, or a number of other issues. Until you get back to back identical checks you still have an issue you need to sort out by any means possible. This also means that you can't rely on the data you read from the array being correct, and you especially should avoid writing to the array, who knows if the data you write will be accurately stored. You must get to the point of repeatable parity checks with zero errors before you can trust the server again.

Take a look at the Unbalance plugin.

One disk at a time. mc at the command line, browse to /mnt/disk1 on one side, /mnt/diskY (destination) on the right, highlight the share name folder on the left, move it to the right. Navigate to /mnt/disk2 on the left, highlight the share, move, etc etc.

Would you say this is a good place to park for a few months? I'm currently still parked at linuxserver/unifi-controller:6.5.55. If you feel this is a good spot, I'll unpin the 6.2.26 post and pin this one.

Try copying everything from the working USB over to the original USB that you registered and see if it boots now.

Why? Parity covers all bits on all drives, used, unused, unformatted, corrupt, doesn't matter. Empty the drives you want to remove by whatever method works for you, then remove them, add the new drives, and set a new config with only the drives you want to keep and rebuild parity from there.

When's the last time you did a memtest for at least 1 full cycle? Are you running your RAM beyond the limits of your CPU / board? Memory timings are kind of like speed ratings on tires, you can get 150+ MPH rated tires on a car that can only can muster 120 going downhill with a tailwind. Just because you have 3200 rated memory, the CPU may only be stable at 2666 or lower.

What speeds are you averaging for large (multi GB) files?

Parity only protects against single drive failure. Data loss can happen many other ways, user error, corruption, malware on systems accessing Unraid, etc. Versioned backups on physically separate media is the only protection from many of those problems.

Yes, although that requires some assumptions about the stability of your equipment. If you have an unclean shutdown, you probably have at least a few bytes that didn't get updated properly. That's why an unclean shutdown is always followed by a mandatory parity check on the next boot. Another issue is a drive that is hardly ever read going bad silently in the background. Because Unraid spins down drives until they are needed, you can conceivably go months between spinning up a drive, and you wouldn't know it was bad until it was too late. A regularly scheduled parity check ensures that the full capacity of all drives is able to be read error free, ensuring that an unexpected drive failure should be able to be rebuilt. Even completely "empty" drives are fully used end to end in the parity computation, so having one completely empty drive fail while rebuilding a different disk will cause data loss.

Not that I'm aware of.

Not that I'm aware of. Your best bet if you must use USB mass storage with Unraid is to use them as single device pools, so the random disconnects will hopefully not cause data loss. USB devices in the parity protected array are a huge headache.

Depends on the specific hardware.

https://www.dolphindatalab.com/one-click-to-clear-hard-drive-smart/

Preclear is NEVER required. It's purely a means to thoroughly test a drive, and optionally speed up the process if you are adding the drive to a NEW (not replacement) data slot in an already valid parity array. Unraid will automatically clear (not preclear) a drive assigned to an additional data slot, but if a valid preclear signature is found on the drive, Unraid will skip the clearing phase and immediately offer to format the new drive slot, saving several hours. Rebuilding a drive always writes the emulated image to the entire capacity of the drive, regardless of the content of the drive, cleared or otherwise. Reallocated sectors are not necessarily fatal, but depending on how many and if they are increasing it may be a sign of impending failure. A small number that doesn't increase over time is probably fine.

This.

You must change the listening port in the application itself, not in any docker container config option.

Likely yes, try running a long smart test and see if it changes. A single point in time with those stats isn't very meaningful, you need a trend, so multiple data points over time, with the drive being used during that time.

Yes, assuming neither setup had RAID configured that mangles the drive ID.

Can you manually insert it?