Ok yeah that is fairly similar to my setup, except I only have two drives in each host.

In my case I created completely separate data volume, one per drive. You could do the same, three data volumes for storage @ 7TB each for example. On one of the volumes you'll need to split off 100Gb volume for engine, So you'd end up with something like 2 x 7Tb data volumes, 100Gb engine and 6.9TB data volume or something along those lines.

With multiple non-raided drives I'm not sure if this is the best approach or if it makes more sense to software raid the drives first. Personally I like the fact that my volumes are separated.