With diff lock off, one tire will spin and that's it.
With diff lock on, two tires will spin. One in the front, one in the back.

For all to spin, you would need a differential lock - like a Mopar positraction.

Yeah, this is 4 wheel drive
But the wheel with the least traction will break free and spin.

In snow or stuck - you need to put in the diff lock which then transmits power to the front diff and the back diff.

On the front and back diffs, one wheel will spin only - cause they are differentials.

There are actually three differentials.

Power goes to the transfer case - which is a differential.
You can lock the transfer case or not with the diff lock.
IF the transfer case is locked, power goes out both shafts - to the front or back -
no questions asked.

If the transfer case is not locked, power goes out to the front diff or the rear diff - and if one of those spins, then power to the front or back wheels is interrupted by the slip on the set which is spinning.

A ford truck with diff lock at the front and rear diffs is really better in many ways for snow.

You can probably buy a locking diff hub for the Discovery.

Then like a ford, you go out, lock ALL THE wheels lock the center transfer case/diff
then ALL will have power and spin in the snow.

 

You dont want full lockup in your 3rd members with snow and ice...= slide off the road.

 

Hank- if it makes you feel any better, I've had to pull 2 people out of my driveway this past week and one was the snow plow guy...2010 F350. He felt very small afterwards.

 

As someone on here says, in a D2 you can get stuck in places no-one else can reach.