itimpi

If the Extended SMART test fails then the dtive should be replaced.

I have never heard of a list being available.  

You may find this section of the online documentation useful in sorting out your array drives.

In theory it is safe to use a disk with reallocated sectors as long as the value is stable and not increasing.   Having said that there are more on that disk than I would be happy with.

Should not need to do this.   Once you get in I would expect everything to come back as it was before.

Whichever is most convenient.   Normally All but that is up to you as you are then going to make changes.    The New Config tool 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 release notes for the 6.12.0 release described the new naming for the share settings and how they map to the old naming.
 
With the settings you have you should just disable the docker and vm services under Settings and then start Mover manually from the Main tab.  You need to disable the services as they keep files in the ‘system’ share open which will stop them being moved.   When the files have been moved you can reenable the services.   At that point if all the files are on the cache you can set the secondary storage to No.   You might also want Exclusive mode access (also defined in the release notes) for maximum performance.
 
It is not normally necessary to have the isos share on the cache but it does no damage.

Just to clarify, I think you mean the disk is shown as disabled (has a red ‘x’ against it) rather than it is not seen by Unraid?    This distinction is important as a disk is disabled if a write to it fails for any reason as it is no longer in step with parity.    It does NOT mean that the drive had failed, as the commonest reason for a write failing is when the cabling to the drive (either power or SATA) is not perfect.    The SMART report for the drive shows there have been quite a few CRC errors which are ones where a problem was detected when transferring the data to the drive so it is quite likely this is the cause.   If you want to do a test of the drive you can try running an Extended SMART test on the drive.
 
To clear the disabled state one needs to rebuild the drive contents.  Rebuilding of drives 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.   At the moment Unraid is ‘emulating’ disk2 using the combination of the other data drive(s) plus parity so you can see what would be rebuilt (although it looks as if the emulated drive is basically empty).   If you think the drive is OK then you can try rebuilding to itself as described in the link.

It looks like you have it bound to vfio which hides it from Unraid.    Try deleting or renaming the cpnfig/vfio.cfg file on the flash drive if you want Unraid to see it and then reboot the system.

Yes - it has to be 2 steps.   Which one you do first is up to you.

With those settings nothing is going to be recorded as those settings just set up the server to be listening.  There are 2 ways to get something recorded:
use the Mirror to Flash option (normally the easiest).   In this case the results are put into the ‘logs’ folder on the flash drive.. put the IP address of the Unraid server into the Remote syslog server setting.   In this case the results are put into folder specified in the settings.

I would expect it is most likely to be a mapping in a container that needs fixing.

This is not an option in the current Unraid releases as you cannot move files between pools - only to/from a pool and the main Unraid array.
 
it is likely that this restriction will disappear in the Unraid 6.13 release where we have been told that the current Unraid array becomes just another pool type, but there is no ETA when this will be available, and there is always the chance that things do not turn out as expected.

You probably want to use the process documented 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.

Not as you describe.   A file is meant to only be in one place, either array or a pool.   The closest you will get is using a plugin like Appdata Backup to periodically backup the appdata share to another location on the array.
 

Unraid only supports a file being in 1 location (I.e. on a pool OR on the array) at a given point in time.

Since Preclear is not a standard part of Unraid the rebuild process does not check whether the disk has a Preclear signature.    I agree that it could as an optimisation but that would be a new feature/enhancement.

I do not think that Unraid will let you add a new parity and a new array disk in one step so you would need to do them one after the other (in any order).

What you did would work but is a bit error prone.
 
A better process is something like
Use Tools->New Config and select the option to keep all assignments return to the Main tab and change the drive assigned to cache if you parity, check the Parity is Valid checkbox to avoid rebuilding parity.   You can then ignore the warning about overwriting parity as it does not take into account you checked this option. start the array and then format (if needed) the new cache drive.

Looks like it has a old firmware version, so you might want to consider updating it to the most recent version. 

This is all configurable.
 
You can individually configure for each share which pool (if any) is used for caching purposes. 
You can also configure where docker containers and VMs should be placed.
 
You can change things around later if you change your mind about where things should go, although depending on the change made you may then have to manually move some data to match the new setup.

That is normal.   It indicates how much of the ZFS Arc us being used.

You cannot do that using ZFS.  You would have to replace both drives at the same time which means any existing data first has to be copied elsewhere.   This is one reason for using BTRFS in pools - it is much more flexible about adding drives (particularly of mixed sizes).

If it replaces a drive then it will be rebuilt with that drives contents.   Its current contents are irrelevant as the rebuild process overwrites every sector in the drive.  
 
If it is added as a new drive then any existing contents will first be cleared so again any existing content is irrelevant.

Click on the pool on the Main tab and change it to use the Single profile.