So DP supports pool hierarchies, i.e., a Pool can act like it is a HDD that is part of a (other) Pool. This was done especially for me. Just kidding. To make DP and CloudDrive (CD) work together well (but it helps me too). In the CD case, suppose you have two HDDs that are Pooled and you use x2 duplication. You also add a CD to that Pool. What you *want* is one duplicate on either HDD and the other duplicate on the CD. But there is no guarantee it will be that way. Both duplicated could end up at one of the HDDs. Lose the system and you lose all as there is no duplicate on CD.
To solve this, add both HDDs to Pool A. This Pool is not duplicated. You also have CD (or another Pool of a number of HDDs) and create unduplicated Pool B witrh that. If you then create a duplicated Pool C by adfding Pool A and Pool B, then DP, through Pool C will ensure that one duplicate ends up at (HDDs) in Pool A and the other duplicate will en up at Pool B. This is becuase DP will, for the purpose of Pool C, view Pool A and Pool B as single HDDs and DP ensures that duplicates are not stored on the same "HDD".
Next, for backup purposes, you would backup the underlying HDDs of Pool A and you would be backing up only one duplicate and still be certain you have all files.
Edit: In my case, this allows me to backup a single 4TB HDD (that is partitioned into 2 2TB partitions) in WHS2011 (which onyl supports backups of volumes/partitions up to 2TB) and still have this duplicated with another 4TB HDD. So, I have:
Pool A: 1 x 4TB HDD, partitioned into 2 x 2TB volumes, both added, not duplicated
Pool B: 1 x 4TB HDD, partitioned into 2 x 2TB volumes, both added, not duplicated
Pool C: Pool A + Pool B, duplicated.
So, every file in Pool C is written to Pool A and Pool B. It is therefore, at both 4TB HDDs that are in the respective Pools A and B. Next, I backup both partitions of either HDD and I have only one backup with the guarantee of having one copy of each file included in the backup.