Oef... those notifications haven't come in for a while as I had some issues with it and never bothered!
But I was able to use the 'overheat' alerts to determine the slots! (messages were like Jan 2022, but I haven't changed anything since then.)
So Plan now is (as soon as the new usb is in):
Prepare new usb with trial version.
Connect all the disks to the system.
Assign all the disks to there original slots. (including the replacement disk in the slot of disk that is dead)
Start the array (make sure "parity is valid" is checked)
Stop the array
remove/disconnect the replacement drive
Start the array. (this should allow the data to be emulated.)
Retrieve backup of USB
Overwrite contents of the new/trial usb with the contents in the backup.
(reboot the system?)
Start the array, check everything is in working order
stop the array, and assign the replacement disk on the place where the disk dead.
It should start to rebuild the old data.
In step3 I am not sure if you want me to only physically connect the drive or also assign it to the array.
And would I lower the risk of faults using maintenance mode of the array.?
That way it's read only correct? Or is my understanding wrong of the maintenance mode?
Thanks for the help so far!