Hello,
We have more than 2 years running MT v4 an v5 in our main routers (Dell 2950 and 1950) 1950 is the backup today we decided to upgrade the backup to v6 to check and was a total failure it upgraded and booted but could not see any interfaces.
As soon as we hit /interfaces/print the hardware will hang a bit, then ctrl + c to get out after that there was no way to access the server only by console or serial, also when /system/reboot the server will hang in stopping services…, and that’s it. Only removing the electricity will go out of that screen.
To be able to downgrade to v5.25 we had to remove the HDD place it in a desktop load v5.25 and then downgrade. After that booted perfectly fine and all the interfaces and all the server was good to go.
It you have a production Dell 1950 or 2950 do not upgrade to v6 unless is a test environment.