3 -> 6 nodes per DC; Will cut repair time in half?

[Max C.]

Hi -

Our current cluster is 2 DCs, 3 nodes per DC.  16 vnodes.  RF=3

We're looking to expand our cluster to 6 nodes per DC. 

Given the RF=3, it's my hope that Reaper will be able to run 2 segments at once (i.e. at any moment in time 1 segment hitting half of the nodes, other segment hitting the other half), which would then cause the repair to take half of the time.

Is this correct?  Is there any special setup I need to do to ensure that this will happen (ex: rack configuration)?

Thanks.

- Max