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This is a bad sign for disk2:
197 Current_Pending_Sector -O--C- 100 099 000 - 50 so I think the drive should be replaced.   When you add a parity disk then Unraid is unable to recover a failed disk unless all other disks can be read error free.
 
There is also this:
# 1 Extended offline Completed: read failure 90% 34760 1693889040 and we normally say that any drive that cannot pass the Extended SMART test should be replaced.

You could delete the config/vfio.cfg file on the flash drive and reboot.

The New Config option is covered Here in the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page. The Unraid OS->Manual section in particular covers most features of the current Unraid release.
 
i recommend you use the option to keep all current assignment, and then just remove the drive you longer want in the array on the Main tab before starting the array to commit the change.   No need to physically disconnect that drive.   Your dockers, etc will stay installed.

That is definitely the safest thing to do.  You might want to put a clean unRAID install on another USB stick while doing this and boot off that as it will then not have any drives configured.
 
Keep the 'red-balled' disk somewhere safe while doing recovery.  If by any chance anything goes wrong during recovery then as long as the 'red-balled' drive has not physically failed it is highly likely you could recover virtually all of the data off it.

Looking at that SMART report and the syslog entries it looks likely that the drive really has failed.
 
you could try and run an extended SMART test on it (possibly on another system) as if that fails it is normally enough to get a RMA (assuming the drive is still under warranty).

I would expect that you can just delete the file and it would be recreated.

With those settings at the container level, you want to tell Plex to transcode to /transcode.   The docker system will then redirect that to /tmp/plex_transcode at the Unraid level.

Unraid currently requires at least one drive in the array.   If you do not intend to use it to store anything a workaround is to use an old flash drive.

You should:
Disable the Docker service under settings (it needs to be disabled to stop it keeping files open) Run mover to transfer the contents of the 'system' share to the cache (optional) When that completes you might want to confirm that there is now no sign of the 'system' share on disk1  Set the secondary storage option for the 'system' to None Enable the option to use Exclusive shares under Settings->Global Share settings to get the performance advantage of bypassing the Unraid Fuse layer  Reenable the Docker service Once this is done then docker will not be keeping disk1 and parity spun up all the time.

Did not spot anything obvious either!
 
It might be worth installing the File Activity plugin to see if that gives a clue as to what is accessing the drive.

It is most likely to be something you have configured in a docker container.

The reason that 32GB is mentioned is that the flash drive needs to be formatted as FAT32 and Windows does not support as standard doing this on drives over 32GB.   Also Unraid only needs something like 1-2GB on the flash drive so large drives have lots of space that will never be used.

Do you by any chance have the Docker Folder plugin installed?   If so you should remove it (it has been replaced by Folder View).
 
if it is not that you are likely to get better informed feedback if you attach your system’s diagnostics zip file to your next post in this thread.

More often than not when a drive is disabled (because a write failed) it was due to an external factor and the drive is physically OK.

Your screen shot shows you ran a correcting parity check which made the parity agree with the data drives.  Had you by any chance had an unclean shutdown earlier - they would normally cause a few sync errors.   You should then not expect any further errors on the next check
 
Was this a manually initiated check or a scheduled one?   Just asking as we normally recommend that scheduled checks are set to be non-correcting so that faulty hardware will not end up corrupting parity before you are aware of any issues.

That output suggests there is some level of corruption.
 
You ran with the -n option (the no modify flag) so nothing was fixed.    To actually fix it you need to run without -n (and if it asks for it add -L). 
 
After that you can restart the array in normal mode to see if the drive now mounts.   I expect it will, so you then need to look for a lost+found folder which is where the repair process puts any folders/files for which it could not find the directory entry giving the correct name and gives them cryptic names instead.  Not having this folder is a good sign that the repair went perfectly.   However if you DO have that folder you have to sort its contents out manually or restore any missing files from backups (which is normally easiest if your backups are good enough).

If you have User Shares enabled then it is normal for every top level folder on a drive to automatically become a User Share with default settings and Unraid has always worked like this. 

The only mapping you have is to /mnt/user which is where User Shares are mounted.   Local drives mounted by UD appear under  /mnt/disks and remote shares under /mnt/remote.   If you want Krusader to be able to access either of these then you need to add volume mappings to support this.

Yes.
 
Click on the boot device on the Main tab and you can then set the SMB security setting for exporting it as a network share with the level of security you want to apply.

The syslog shows that you have docker set to use macvlan AND have bridging enabled on eth0.  As mentioned in the Release Notes this combination is know to cause system crashes.    You ether need to disable bridging on eth0 or switch docker to using ipvlan networking.
 

I think it should be 0 3 * * *
Note that space is a field separator so there should be 4 spaces between the 5 fields.

Both the links you posted go to obsolete documentation.  The online documentation is accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page. The Unraid OS->Manual section in particular covers most features of the current Unraid release.
 
The section on replacing disks is here.   You will need to upgrade parity first as no data drive can be larger than the smallest parity drive.

Have changed the SMB Export option for the shares you want visible on the network?   The default is No which means they are not visible on the network.

You could use a Trial licence to build out the new machine.
 
On completion you could then copy the 'config' folder for the new machine (except for the trial licence key file) to the flash drive with the Pro licence to transfer the settings of the new machine to it.

The Release Notes mention that if you want to use macvlan then you should disable bridging on eth0 to avoid crashes that can eventually bring down the server.   According to the diagnostics you still have it enabled.