itimpi

I’ve seen lots of reports in the past of SAS drives having issues if you try and spin them down.

You never mention the Minimum Free Space setting which can be relevant in selecting a drive  
 
As to the questions:
Difficult to answer definitively as it can depend on many factors (such as the disk controller), and what Unraid currently has in RAM at the time in terms of directory information.  In ideal conditions only the required drive is spun up. It probably depends on the client.  You will definitely get an out-of-space error for the file that does not fit - whether the others then copy will depend on the client (but they should then go to another drive as long as the share settings allow another drive to be selected. Mover works at the individual file level not the folder level.  At the point it selects a drive a file size of 0 is assumed (and thus the importance of the Minimum Free space setting). If a file already exists then Unraid will always attempt to overwrite it in situ so you get an out-of-space error.   Not quite sure what you meant by Unraid balancing out, but it never moves a file from one array drive to another.

FYI:  I think you mean disk1 in the main Unraid array?   Just checking as that array is not using RAID5 (and hence the name Unraid).
 
In terms of checking/repairing disk1 then the easiest way to proceed is to do it from the GUI as described here in the online documentation.   
 
If you must do it from the command line then you should have used /dev/md1 as the target device since this would preserve parity.   Luckily your command was wrong in that it had the wrong target device (it should have been /dev/sdf1) as that would have invalidated parity.

If a torrent file is initially created without all the space allocated so that it takes additional space as more parts are downloaded this could be a problem as Unraid will not move the file to another drive in such a situation.   It might be worth telling the torrent downloaded to allocate all the space needed for the file at the start to see if that helps alleviate the issue.

Did you check there is no folder for the share on the ‘cache’ device (even if it has no files) as that is sufficient to trigger the warning.

This 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.   once you have gotten the drive out of the array you follow the standard procedure for adding a parity drive.

Not quite - parity2 will remain as parity2 and you will have no parity1.   The calculations for the two parity drives are completely different so they are not interchangeable.   It is perfectly valid to run without parity1 so in that sense parity2 remains valid.
 
regarding step 4 then yes parity remains valid.
 

Not normally - it would keep restarting such operations from the beginning.
 
if you install the Parity Check Tuning plugin then it has the option to resume such operations from the point reached (as long as the shutdown was a tidy one).  0ne restriction (at the moment) is that the array is not auto-started so you have to manually start the array to continue the operation.

XFS does not support multiple drives in the same pool - you have to be using BTRFS to do this.    Switching to BTRFS would involve first copying the existing contents elsewhere (e.g. the main array) and then copying it back after setting up the multi-drive pool as btrfs and formatting the pool drives.  
 
Note that if you have a single drive pool already set up as btrfs you can add additional drives to it and/or change the RAID level without reformatting.

The last set of output says it also had the -n option set although you said you only used -Lv.   Until you run without the -n (no modify) option set nothing will be repaired.  The diagnostics posted seem to agree in that they show there is still corruption on disk1.
 
 

The moment you format a drive you will lose something like 1-2% of the total size as the file system structures are created to hold directory type information.

sounds as if you have misunderstood how parity works on Unraid.
 
1.).  No.   Parity is updated in real-time so after a drive failure you are recovering to the the current data state.
 
2).  It is!    Updating the parity on all writes to the array is the main limiting factor on speeds writing to the array. The parity check process is just an (optional) house-keeping one to check that everything is as it should be.

The ? icon at the top right is a toggle to turn the built in help on/off.  You can also do it for individual fields by clicking on the text describing the field.

If you still have this folder after rebooting, then you still have a docker container configured with this path and thus recreating it.   You need to fix that and then reboot to confirm this is no longer being created.

What makes you think Unraid is saying a disk is 'Bad'?  Disks can go into an error state (i.e. be disabled) at the Unraid level without the disk itself going bad.  Unraid disables a drive if a write fails for any reason,  and there can be a lot of causes for this that are external to the drive itself with the commonest being related to the cabling to the drive.
 
We normally ask users to run an Extended SMART test from within Unraid on drives that are disabled, and only if that fails do we assume the disk itself is at fault.

5 Reallocated_Sector_Ct PO--CK 100 100 010 - 12288 I am surprised that you have not had issues previously with this drive.   A small number of reallocated sectors is normally OK as long as the number remains stable, but a number this large is definitely a sign of trouble.

Since you only have single parity it is possible to re-arrange the order of the drives without invalidating parity.   This would not have been true if you had parity2 as that uses the slot number of part of its calculations.
Use the New Config tool and select the option to retain all current assignments. Make sure you actually click the Apply button and after that click Done.  If you did not use this then Unraid would complain when you tried to move drives to new slots.
return to the main tab and make the changes you want to move the array drives up in slot number. The drives should have blue icons if you did the New Config correctly.
tick the parity is already valid checkbox
start the array to commit the changes
the drives should come up with all their data intact and in the new slots, and Unraid should not be recalculating parity.

You are getting continual resets of several of your drives (showing in logs as ata28, ata29, ata33).   I would carefully check all cabling (power and SATA) to your drives.

That should not be there - the information is persisted in a file of that name.   You may find that deleting that folder means the original drive starts saving the drive settings, but I would be worried that the presence of the folder Indic ated an issue with the drive.

There have been reports of the ‘extra’ space not always being correctly zeroed when upgrading the size of the parity drive (although the exact combination of circumstances to trigger this have not been identified as far as I know).  If the errors only start occurring after you get past the old size of the parity drive then you have almost certainly encountered this.  In such a case the only fix I know of is to run a correcting parity check after which subsequent checks will no longer report the errors.

There is no in-situ conversion.
 
it might be simpler to change the allocation method which then applies for new files and leave those already copied where they are.

It might be worth trying the steps listed here to make the drive bootable in the manual method for making a flash drive.  I have heard of the USB Creator tool not always doing this step properly.

This can happen if you have insufficient space on the flash, or if you have less than 4GB RAM.
 
You can always use the manual method of doing an upgrade in such cases.

Only if you configure the share to have this behaviour.    You can configure a User share to never be put on the main array.

A f;ash drive (pendrive) works fine.   It just needs to be a storage device.