All right, I have managed to be back online
I had to recheck all the disks using an old DOS program DISKPART
Then I re-installed an older version of the firmware (1.06) that I had saved from years ago... I'm not sure I sure load 1.72 since everything is working.
Everything is stable. I have re-created an array with 3x3To drives and the 4th one is set to spare. Like before.
I was not sure if the 3To were supported but the product description did say it was ok.
Thank you for your post, it lead me to the solution. I was ready to get rid of the whole thing.
The problem being that when the TS is stuck on "firmware updating" you cannot connect to the web admin or NasNavigator. So you have the turn it off the hard way, modify the drives, restart to trigger the E/M mode and then you can try something else.
But after each try, you need to verify if the disks were not modified already with partitions.
If so, you need to delete all of it again.
Lucky me I got this USB/SATA converter so I can quickly check all the drives with fdisk
Then I had this one drive which would not allow me to merge 2 partitions... That's when I got to use diskpart. But like it was not enough, it would not allow me to create a single volume afterwards!
Anyway, Now I got this. I hope I don't have to get through this &!@# again.
For the record, I am using a TS-XL/R5 bought in ... 2008 with 4 drives.