Originally posted by reydp
with 3 you might be in trouble if 1 of those redo logs gets STALE status, you left with 2 groups and then I/O contentions comes between LGWR and ARCH process.
That's why I said 4 at most.

So that's why I arrive to have it 5 groups. But that's me. :-))
You will be fine with 4 :-))