itimpi

That looks good.   Can you get anything off the old flash drive?  If so the contents of the ‘config’ folder are what you want.   That would allow you to avoid reconfiguring things as you could then copy its contents to the new flash drive.
 
Regarding changing the licence if you have your original licence file put it in the ‘config’ folder on the new flash drive and when Unraid boots it should take you through the process for transferring the licence to the new drive.  If you have any problems with this then you will need to contact support.
 
It is always a good idea to have a backup of your flash drive.   You can always make one manually either by copying the contents on a PC/Mac or (probably more convenient) clicking on the Boot drive on the Main tab and selecting the backup option.    In terms of automated backups then you can periodically make one locally on the server using the appdata backup plugin, or on the cloud by installing the Unraid connect plugin (used to be called MyServers).

That is expected behaviour if you have Exclusive Shares enabled and meet the conditions on a particular share for it being Exclusive.   The /mnt/cache/xxx path is more efficient than going via /mnt/user/xxx as it bypasses the Fuse layer in Unraid.   This is described in the GUI help for the Exclusive setting under Settings->Global Share Settings

These are automatically created if docker and VMs are enabled.

To get best performance for docker containers and VMs you want this share to be on the cache (i.e. mover to be array->Cache).    
 
You can get even better performance if once the whole share is on the cache you remove the secondary storage option and under Settings->Global Share settings you enable the option for Exclusive Shares as this bypasses the Fuse layer in Unraid that is otherwise used to manage User Shares.

Actually it tells you nothing about the cables as the test is completely internal to the drive.
 
the process for re-enabling the drive 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.
 

Contact support
 

The SMART information for that drive looks very bad as it has lots of reallocated and pending sectors - both of which you really want to be 0 for reliable operation in Unraid.   I would replace ASAP.

You will need to contact support.

you might want to try removing the Mover Tuning plugin and then rebooting as it seems to have recently been causing problems with mover operating as expected.

This is the normal action at this point as Unraid has already failed to mount the drive.    Normally the -L option causes no data loss, and even when it does it is only the last file being written that tends to have a problem.
 
The section of the the online documentation accessible via the Manual link at the bottom of the Unraid GUI has this section covering repair and it mentions you should use the -L option in point 5.

There is no obvious error showing in the SMART reports but you could rerun an extended SMART test to be sure.   More often than not it is an issue with either the SATA cabling or power to the dtive so worth checking these are well seated.
 
Your syslog is being ‘spammed’ with autofan messages which makes it very difficult to find anything else useful there.   I would you suggest you either adjust the autofan settings to get less messages in the syslog (or perhaps even disable it completely) and get new diagnostics to see if we can spot anything.

You can go to Apps->Previous Apps to reinstall docker containers using their previous settings

If a drive will not pass a Preclear then you should not use the drive.   If a drive fails during normal use of the array then Unraid requires all the remaining drives to be able to read error free to recover the contents if a failed drives.  
 
Pending sectors are never a good sign although it is possible that they can get reset to 0 during the Preclear process.
 
as an alternative to pre-clear you can run the extended SMART test on the drives.    If this fails a drive should not be used.

It will be because one of them is using TB units while the other is using TiB units (i.e binary v decimal).
 

The parity drive has been disabled which means a write to it failed so Unraid has stopped using it and is now merely performing a read check on the other drives so probably no reason to continue.
 
The parity drive is showing a lot of reallocated sectors (832) so I suspect it may be a genuine problem with the drive and it will need replacing rather than our normal first suspect of being the power or sata cabling to the drive.   You could try running an extended SMART test on the drive to see if that passes as if it does not the drive definitely needs replacing.

If the process you outlined here does not complete then it strongly suggests there really is a problem with the drive and it may need replacing.   No point in resetting the array configuration if the rebuild continually fails until you have a replacement.    
 
Having said that I would carefully first check the cabling to the drive, especially the power side and avoid using power splitters if possible because as was mentioned earlier cabling is a far more common that physical failure of a drive.

There are a lot of pending sectors and the reallocated sector count for that drive is very high so I would think it really is failing.   The reallocation of sectors is internal to the drive so it seems very unlikely to be the HBA.  The only think that just might contribute to this that I can think of would be power related issues.  Much more likely I would think is that the drive got damaged in transit.
 

Have you checked that you do not have the Export setting for the shares set to No (which is the default).   You need one of the other settings for them to be visible on the network.

I expect this is just the difference between TB and TiB values.

You should make sure that the Minimum Free Space value on the cache is set to be more than the largest file you want cached to avoid it ever completely filling up and causing problems.

You currently have the number of array devices set to be a max of 3.   You need to increase that if you want to add more drives.

Enable the syslog server. 

No problem doing what you mention, and in fact checking out Unraid satisfies your needs before you commit to buying it is always recommended.

Alternatively try the Manual install method.    Unraid does not use GRUB so the message you showed definitely means the flash drive was not correctly created.

Sounds as if the docker.img file may have been reset as the diagnostics show it to basically be empty? 
 
Simply restoring the appdata will not do anything if the system thinks no dockers are installed - it simply puts the working data back for containers but you still need the containers to be installed.
 
You can reinstall containers with their previous settings intact by using Apps->Previous Apps.