trurl

No
 

New Config resets super.dat (your array assignments) so that is OK. 
 
Better if you start in normal mode instead of maintenance mode. We can't tell anything about your filesystems in maintenance mode.

Do you have a current flash backup? 
 
The config folder is all you need to get your configuration going on whichever version you download 

Test like this first to see if it boots:
then
If that doesn't boot, then try SAFE mode to eliminate plugins

No point in formatting a drive before preclearing it. Format writes an empty filesystem to the disk (that is what format actually means in all OS). Then preclear would wipe that empty filesystem out completely by overwriting the entire disk with zeros.
 
And you don't need a clear disk to replace a failed disk.
 
If you want to test a disk by preclearing it, install Unassigned Devices and Unassigned Devices Preclear plugins.

Reboot

I've never used ZFS in the parity array.
 
yes
 

SMART for disk5 looks OK, and emulated disk5 is mounted with lots of data.
 
syslog-previous seems to indicate a connection problem.
 
Rebuilding was always the correct thing to do anyway. The disk was kicked out of the array because a write to it had failed, but that initial failed write and all subsequent writes were emulated by updating parity. So the physical disk is out-of-sync and missing some writes.
 
You might check connections before starting the rebuild.

Ideally no more than 4 disks per PSU cable.

Click the FIX button

All write operations in the array update parity at the same time. Write, copy, move, delete are all write operations.
 
Format is also a write operation. It writes an empty filesystem to the disk. So, after format, parity agrees the disk has an empty filesystem.
 
You might as well go ahead and let it rebuild the empty filesystem unless you want to remove the disk and New Config/Rebuild Parity without anything assigned to that slot.

Tools - New Permissions on just the user share(s) affected. DO NOT do New Permissions on appdata.
 
How were these folders/files created?

Looks like it was kicked out again almost immediately after starting rebuild. Emulated disk3 is mounted.
 
Do you have a spare disk you could use for rebuild?

Why do you have so many user shares?
 
You have to go to each of your user shares and make sure none specify cache instead of mypool. Simple as that.

https://docs.unraid.net/unraid-os/manual/docker-management/#re-create-the-docker-image-file
 
https://docs.unraid.net/unraid-os/manual/docker-management/#re-installing-docker-applications
 
https://docs.unraid.net/unraid-os/manual/docker-management/#docker-custom-networks

That looks OK.
 
Reboot and post diagnostics.

Check connections, SATA and power, both ends, including splitters.
 
Not sure where you get that idea.
 
https://docs.unraid.net/unraid-os/manual/storage-management/#rebuilding-a-drive-onto-itself
 
 

Removing the drive won't change anything, since it is disabled/emulated it isn't being used at all currently. Where removing it could cause problems, including when you do finally replace it, is if you disturb any other connections.
 
Unrelated, you have a lot of .cfg files in config/shares on your flash drive for shares that don't exist. These are the settings for user shares you no longer have. Possibly you accidentally created a lot of shares by writing to the top level of disks or pools. Now these shares don't exist because there are no top level folders with those names. You can clean those up (and clean up your diagnostics) by clicking the CLEAN UP button on the User Shares page.

Maybe this plugin?
 

user is wrong. Have to wonder how you got it that way. Probably something you did at the command line as root.
 
Do this:
chmod 777 /mnt/user chown nobody:users /mnt/user  
 

Apr 12 19:27:56 RR-Tower sshd-session[1471095]: Starting session: command for root from 192.168.1.100 port 58290 id 1 Apr 12 19:27:56 RR-Tower sshd-session[1471095]: Close session: user root from 192.168.1.100 port 58290 id 4 Do you know why your syslog has so many of these entries, several times per second? Can you make it stop?

That should work.
 
The array assignments are in config/super.dat
 
The pool assignments are in config/pools

Try Tools - New Permissions on only that user share.

Doesn't look like disk6 was ever included in your New Config. And the 4/16 diagnostics seems to confirm that.
 
Let's try again.
 
New Config - Retain All - Apply
Assign disk6
Check BOTH Parity Valid AND Maintenance mode checkboxes.
Start the array.
Stop the array.
Unassign disk6.
Start the array in normal (not maintenance) mode with disk6 unassigned.
Post new diagnostics.